diff options
Diffstat (limited to 'runtime/relayfs')
| -rw-r--r-- | runtime/relayfs/Makefile | 12 | ||||
| -rw-r--r-- | runtime/relayfs/buffers.c | 195 | ||||
| -rw-r--r-- | runtime/relayfs/buffers.h | 12 | ||||
| -rwxr-xr-x | runtime/relayfs/build | 4 | ||||
| -rw-r--r-- | runtime/relayfs/inode.c | 423 | ||||
| -rw-r--r-- | runtime/relayfs/linux/relayfs_fs.h | 263 | ||||
| -rw-r--r-- | runtime/relayfs/relay.c | 530 | ||||
| -rw-r--r-- | runtime/relayfs/relay.h | 12 | ||||
| -rw-r--r-- | runtime/relayfs/relayfs.txt | 206 |
9 files changed, 1657 insertions, 0 deletions
diff --git a/runtime/relayfs/Makefile b/runtime/relayfs/Makefile new file mode 100644 index 00000000..220a4e32 --- /dev/null +++ b/runtime/relayfs/Makefile @@ -0,0 +1,12 @@ +# +# relayfs Makefile +# + +CFLAGS += -I $(RELAYFS_INCLUDE) + +obj-m += relayfs.o + +relayfs-y := relay.o inode.o buffers.o + +clean: + /bin/rm -rf *.o *.ko *~ *.mod.c .*.cmd .tmp_versions diff --git a/runtime/relayfs/buffers.c b/runtime/relayfs/buffers.c new file mode 100644 index 00000000..476eafd8 --- /dev/null +++ b/runtime/relayfs/buffers.c @@ -0,0 +1,195 @@ +/* + * RelayFS buffer management code. + * + * Copyright (C) 2002-2005 - Tom Zanussi (zanussi@us.ibm.com), IBM Corp + * Copyright (C) 1999-2005 - Karim Yaghmour (karim@opersys.com) + * + * This file is released under the GPL. + */ + +#include <linux/module.h> +#include <linux/vmalloc.h> +#include <linux/mm.h> +#include <linux/relayfs_fs.h> +#include "relay.h" +#include "buffers.h" + +/* + * close() vm_op implementation for relayfs file mapping. + */ +static void relay_file_mmap_close(struct vm_area_struct *vma) +{ + struct rchan_buf *buf = vma->vm_private_data; + buf->chan->cb->buf_unmapped(buf, vma->vm_file); +} + +/* + * nopage() vm_op implementation for relayfs file mapping. + */ +static struct page *relay_buf_nopage(struct vm_area_struct *vma, + unsigned long address, + int *type) +{ + struct page *page; + struct rchan_buf *buf = vma->vm_private_data; + unsigned long offset = address - vma->vm_start; + + if (address > vma->vm_end) + return NOPAGE_SIGBUS; /* Disallow mremap */ + if (!buf) + return NOPAGE_OOM; + + page = vmalloc_to_page(buf->start + offset); + if (!page) + return NOPAGE_OOM; + get_page(page); + + if (type) + *type = VM_FAULT_MINOR; + + return page; +} + +/* + * vm_ops for relay file mappings. + */ +static struct vm_operations_struct relay_file_mmap_ops = { + .nopage = relay_buf_nopage, + .close = relay_file_mmap_close, +}; + +/** + * relay_mmap_buf: - mmap channel buffer to process address space + * @buf: relay channel buffer + * @vma: vm_area_struct describing memory to be mapped + * + * Returns 0 if ok, negative on error + * + * Caller should already have grabbed mmap_sem. + */ +int relay_mmap_buf(struct rchan_buf *buf, struct vm_area_struct *vma) +{ + unsigned long length = vma->vm_end - vma->vm_start; + struct file *filp = vma->vm_file; + + if (!buf) + return -EBADF; + + if (length != (unsigned long)buf->chan->alloc_size) + return -EINVAL; + + vma->vm_ops = &relay_file_mmap_ops; + vma->vm_private_data = buf; + buf->chan->cb->buf_mapped(buf, filp); + + return 0; +} + +/** + * relay_alloc_buf - allocate a channel buffer + * @buf: the buffer struct + * @size: total size of the buffer + * + * Returns a pointer to the resulting buffer, NULL if unsuccessful + */ +static void *relay_alloc_buf(struct rchan_buf *buf, unsigned long size) +{ + void *mem; + int i, j, n_pages; + + size = PAGE_ALIGN(size); + n_pages = size >> PAGE_SHIFT; + + buf->page_array = kcalloc(n_pages, sizeof(struct page *), GFP_KERNEL); + if (!buf->page_array) + return NULL; + + for (i = 0; i < n_pages; i++) { + buf->page_array[i] = alloc_page(GFP_KERNEL); + if (unlikely(!buf->page_array[i])) + goto depopulate; + } + mem = vmap(buf->page_array, n_pages, GFP_KERNEL, PAGE_KERNEL); + if (!mem) + goto depopulate; + + memset(mem, 0, size); + buf->page_count = n_pages; + return mem; + +depopulate: + for (j = 0; j < i; j++) + __free_page(buf->page_array[j]); + kfree(buf->page_array); + return NULL; +} + +/** + * relay_create_buf - allocate and initialize a channel buffer + * @alloc_size: size of the buffer to allocate + * @n_subbufs: number of sub-buffers in the channel + * + * Returns channel buffer if successful, NULL otherwise + */ +struct rchan_buf *relay_create_buf(struct rchan *chan) +{ + struct rchan_buf *buf = kcalloc(1, sizeof(struct rchan_buf), GFP_KERNEL); + if (!buf) + return NULL; + + buf->padding = kmalloc(chan->n_subbufs * sizeof(unsigned *), GFP_KERNEL); + if (!buf->padding) + goto free_buf; + + buf->commit = kmalloc(chan->n_subbufs * sizeof(unsigned *), GFP_KERNEL); + if (!buf->commit) + goto free_buf; + + buf->start = relay_alloc_buf(buf, chan->alloc_size); + if (!buf->start) + goto free_buf; + + buf->chan = chan; + kref_get(&buf->chan->kref); + return buf; + +free_buf: + kfree(buf->commit); + kfree(buf->padding); + kfree(buf); + return NULL; +} + +/** + * relay_destroy_buf - destroy an rchan_buf struct and associated buffer + * @buf: the buffer struct + */ +void relay_destroy_buf(struct rchan_buf *buf) +{ + struct rchan *chan = buf->chan; + int i; + + if (likely(buf->start)) { + vunmap(buf->start); + for (i = 0; i < buf->page_count; i++) + __free_page(buf->page_array[i]); + kfree(buf->page_array); + } + kfree(buf->padding); + kfree(buf->commit); + kfree(buf); + kref_put(&chan->kref, relay_destroy_channel); +} + +/** + * relay_remove_buf - remove a channel buffer + * + * Removes the file from the relayfs fileystem, which also frees the + * rchan_buf_struct and the channel buffer. Should only be called from + * kref_put(). + */ +void relay_remove_buf(struct kref *kref) +{ + struct rchan_buf *buf = container_of(kref, struct rchan_buf, kref); + relayfs_remove(buf->dentry); +} diff --git a/runtime/relayfs/buffers.h b/runtime/relayfs/buffers.h new file mode 100644 index 00000000..37a12493 --- /dev/null +++ b/runtime/relayfs/buffers.h @@ -0,0 +1,12 @@ +#ifndef _BUFFERS_H +#define _BUFFERS_H + +/* This inspired by rtai/shmem */ +#define FIX_SIZE(x) (((x) - 1) & PAGE_MASK) + PAGE_SIZE + +extern int relay_mmap_buf(struct rchan_buf *buf, struct vm_area_struct *vma); +extern struct rchan_buf *relay_create_buf(struct rchan *chan); +extern void relay_destroy_buf(struct rchan_buf *buf); +extern void relay_remove_buf(struct kref *kref); + +#endif/* _BUFFERS_H */ diff --git a/runtime/relayfs/build b/runtime/relayfs/build new file mode 100755 index 00000000..a0eece3a --- /dev/null +++ b/runtime/relayfs/build @@ -0,0 +1,4 @@ +#!/bin/bash + +make V=1 -C /lib/modules/`uname -r`/build M=`pwd` modules \ + RELAYFS_INCLUDE=`pwd` diff --git a/runtime/relayfs/inode.c b/runtime/relayfs/inode.c new file mode 100644 index 00000000..da32b7d2 --- /dev/null +++ b/runtime/relayfs/inode.c @@ -0,0 +1,423 @@ +/* + * VFS-related code for RelayFS, a high-speed data relay filesystem. + * + * Copyright (C) 2003-2005 - Tom Zanussi <zanussi@us.ibm.com>, IBM Corp + * Copyright (C) 2003-2005 - Karim Yaghmour <karim@opersys.com> + * + * Based on ramfs, Copyright (C) 2002 - Linus Torvalds + * + * This file is released under the GPL. + */ + +#include <linux/module.h> +#include <linux/fs.h> +#include <linux/mount.h> +#include <linux/pagemap.h> +#include <linux/init.h> +#include <linux/string.h> +#include <linux/backing-dev.h> +#include <linux/namei.h> +#include <linux/poll.h> +#include <linux/relayfs_fs.h> +#include "relay.h" +#include "buffers.h" + +#define RELAYFS_MAGIC 0xF0B4A981 + +static struct vfsmount * relayfs_mount; +static int relayfs_mount_count; +static kmem_cache_t * relayfs_inode_cachep; + +static struct backing_dev_info relayfs_backing_dev_info = { + .ra_pages = 0, /* No readahead */ + .memory_backed = 1, /* Does not contribute to dirty memory */ +}; + +static struct inode *relayfs_get_inode(struct super_block *sb, int mode, + struct rchan *chan) +{ + struct rchan_buf *buf = NULL; + struct inode *inode; + + if (S_ISREG(mode)) { + BUG_ON(!chan); + buf = relay_create_buf(chan); + if (!buf) + return NULL; + } + + inode = new_inode(sb); + if (!inode) { + relay_destroy_buf(buf); + return NULL; + } + + inode->i_mode = mode; + inode->i_uid = 0; + inode->i_gid = 0; + inode->i_blksize = PAGE_CACHE_SIZE; + inode->i_blocks = 0; + inode->i_mapping->backing_dev_info = &relayfs_backing_dev_info; + inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME; + switch (mode & S_IFMT) { + case S_IFREG: + inode->i_fop = &relayfs_file_operations; + RELAYFS_I(inode)->buf = buf; + break; + case S_IFDIR: + inode->i_op = &simple_dir_inode_operations; + inode->i_fop = &simple_dir_operations; + + /* directory inodes start off with i_nlink == 2 (for "." entry) */ + inode->i_nlink++; + break; + default: + break; + } + + return inode; +} + +/** + * relayfs_create_entry - create a relayfs directory or file + * @name: the name of the file to create + * @parent: parent directory + * @mode: mode + * @chan: relay channel associated with the file + * + * Returns the new dentry, NULL on failure + * + * Creates a file or directory with the specifed permissions. + */ +static struct dentry *relayfs_create_entry(const char *name, + struct dentry *parent, + int mode, + struct rchan *chan) +{ + struct qstr qname; + struct dentry *d; + struct inode *inode; + int error = 0; + + BUG_ON(!name || !(S_ISREG(mode) || S_ISDIR(mode))); + + error = simple_pin_fs("relayfs", &relayfs_mount, &relayfs_mount_count); + if (error) { + printk(KERN_ERR "Couldn't mount relayfs: errcode %d\n", error); + return NULL; + } + + qname.name = name; + qname.len = strlen(name); + qname.hash = full_name_hash(name, qname.len); + + if (!parent && relayfs_mount && relayfs_mount->mnt_sb) + parent = relayfs_mount->mnt_sb->s_root; + + if (!parent) { + simple_release_fs(&relayfs_mount, &relayfs_mount_count); + return NULL; + } + + parent = dget(parent); + down(&parent->d_inode->i_sem); + d = lookup_hash(&qname, parent); + if (IS_ERR(d)) { + d = NULL; + goto release_mount; + } + + if (d->d_inode) { + d = NULL; + goto release_mount; + } + + inode = relayfs_get_inode(parent->d_inode->i_sb, mode, chan); + if (!inode) { + d = NULL; + goto release_mount; + } + + d_instantiate(d, inode); + dget(d); /* Extra count - pin the dentry in core */ + + if (S_ISDIR(mode)) + parent->d_inode->i_nlink++; + + goto exit; + +release_mount: + simple_release_fs(&relayfs_mount, &relayfs_mount_count); + +exit: + up(&parent->d_inode->i_sem); + dput(parent); + return d; +} + +/** + * relayfs_create_file - create a file in the relay filesystem + * @name: the name of the file to create + * @parent: parent directory + * @mode: mode, if not specied the default perms are used + * @chan: channel associated with the file + * + * Returns file dentry if successful, NULL otherwise. + * + * The file will be created user r on behalf of current user. + */ +struct dentry *relayfs_create_file(const char *name, struct dentry *parent, + int mode, struct rchan *chan) +{ + if (!mode) + mode = S_IRUSR; + mode = (mode & S_IALLUGO) | S_IFREG; + + return relayfs_create_entry(name, parent, mode, chan); +} + +/** + * relayfs_create_dir - create a directory in the relay filesystem + * @name: the name of the directory to create + * @parent: parent directory, NULL if parent should be fs root + * + * Returns directory dentry if successful, NULL otherwise. + * + * The directory will be created world rwx on behalf of current user. + */ +struct dentry *relayfs_create_dir(const char *name, struct dentry *parent) +{ + int mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO; + return relayfs_create_entry(name, parent, mode, NULL); +} + +/** + * relayfs_remove - remove a file or directory in the relay filesystem + * @dentry: file or directory dentry + */ +int relayfs_remove(struct dentry *dentry) +{ + struct dentry *parent = dentry->d_parent; + if (!parent) + return -EINVAL; + + parent = dget(parent); + down(&parent->d_inode->i_sem); + if (dentry->d_inode) { + simple_unlink(parent->d_inode, dentry); + d_delete(dentry); + } + dput(dentry); + up(&parent->d_inode->i_sem); + dput(parent); + + simple_release_fs(&relayfs_mount, &relayfs_mount_count); + + return 0; +} + +/** + * relayfs_remove_dir - remove a directory in the relay filesystem + * @dentry: directory dentry + * + * Returns 0 if successful, negative otherwise. + */ +int relayfs_remove_dir(struct dentry *dentry) +{ + if (!dentry) + return -EINVAL; + + return relayfs_remove(dentry); +} + +/** + * relayfs_open - open file op for relayfs files + * @inode: the inode + * @filp: the file + * + * Increments the channel buffer refcount. + */ +int relayfs_open(struct inode *inode, struct file *filp) +{ + struct rchan_buf *buf = RELAYFS_I(inode)->buf; + kref_get(&buf->kref); + + return 0; +} + +/** + * relayfs_mmap - mmap file op for relayfs files + * @filp: the file + * @vma: the vma describing what to map + * + * Calls upon relay_mmap_buf to map the file into user space. + */ +int relayfs_mmap(struct file *filp, struct vm_area_struct *vma) +{ + struct inode *inode = filp->f_dentry->d_inode; + return relay_mmap_buf(RELAYFS_I(inode)->buf, vma); +} + +/** + * relayfs_poll - poll file op for relayfs files + * @filp: the file + * @wait: poll table + * + * Poll implemention. + */ +unsigned int relayfs_poll(struct file *filp, poll_table *wait) +{ + unsigned int mask = 0; + struct inode *inode = filp->f_dentry->d_inode; + struct rchan_buf *buf = RELAYFS_I(inode)->buf; + + if (buf->finalized) + return POLLERR; + + if (filp->f_mode & FMODE_READ) { + poll_wait(filp, &buf->read_wait, wait); + if (!relay_buf_empty(buf)) + mask |= POLLIN | POLLRDNORM; + } + + return mask; +} + +/** + * relayfs_release - release file op for relayfs files + * @inode: the inode + * @filp: the file + * + * Decrements the channel refcount, as the filesystem is + * no longer using it. + */ +int relayfs_release(struct inode *inode, struct file *filp) +{ + struct rchan_buf *buf = RELAYFS_I(inode)->buf; + kref_put(&buf->kref, relay_remove_buf); + + return 0; +} + +/** + * relayfs alloc_inode() implementation + */ +static struct inode *relayfs_alloc_inode(struct super_block *sb) +{ + struct relayfs_inode_info *p = kmem_cache_alloc(relayfs_inode_cachep, SLAB_KERNEL); + if (!p) + return NULL; + p->buf = NULL; + + return &p->vfs_inode; +} + +/** + * relayfs destroy_inode() implementation + */ +static void relayfs_destroy_inode(struct inode *inode) +{ + if (RELAYFS_I(inode)->buf) + relay_destroy_buf(RELAYFS_I(inode)->buf); + + kmem_cache_free(relayfs_inode_cachep, RELAYFS_I(inode)); +} + +static void init_once(void *p, kmem_cache_t *cachep, unsigned long flags) +{ + struct relayfs_inode_info *i = p; + if ((flags & (SLAB_CTOR_VERIFY | SLAB_CTOR_CONSTRUCTOR)) == SLAB_CTOR_CONSTRUCTOR) + inode_init_once(&i->vfs_inode); +} + +struct file_operations relayfs_file_operations = { + .open = relayfs_open, + .poll = relayfs_poll, + .mmap = relayfs_mmap, + .release = relayfs_release, +}; + +static struct super_operations relayfs_ops = { + .statfs = simple_statfs, + .drop_inode = generic_delete_inode, + .alloc_inode = relayfs_alloc_inode, + .destroy_inode = relayfs_destroy_inode, +}; + +static int relayfs_fill_super(struct super_block * sb, void * data, int silent) +{ + struct inode *inode; + struct dentry *root; + int mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO; + + sb->s_blocksize = PAGE_CACHE_SIZE; + sb->s_blocksize_bits = PAGE_CACHE_SHIFT; + sb->s_magic = RELAYFS_MAGIC; + sb->s_op = &relayfs_ops; + inode = relayfs_get_inode(sb, mode, NULL); + + if (!inode) + return -ENOMEM; + + root = d_alloc_root(inode); + if (!root) { + iput(inode); + return -ENOMEM; + } + sb->s_root = root; + + return 0; +} + +static struct super_block * relayfs_get_sb(struct file_system_type *fs_type, + int flags, const char *dev_name, + void *data) +{ + return get_sb_single(fs_type, flags, data, relayfs_fill_super); +} + +static struct file_system_type relayfs_fs_type = { + .owner = THIS_MODULE, + .name = "relayfs", + .get_sb = relayfs_get_sb, + .kill_sb = kill_litter_super, +}; + +static int __init init_relayfs_fs(void) +{ + int err; + + relayfs_inode_cachep = kmem_cache_create("relayfs_inode_cache", + sizeof(struct relayfs_inode_info), 0, + 0, init_once, NULL); + if (!relayfs_inode_cachep) + return -ENOMEM; + + err = register_filesystem(&relayfs_fs_type); + if (err) + kmem_cache_destroy(relayfs_inode_cachep); + + return err; +} + +static void __exit exit_relayfs_fs(void) +{ + unregister_filesystem(&relayfs_fs_type); + kmem_cache_destroy(relayfs_inode_cachep); +} + +module_init(init_relayfs_fs) +module_exit(exit_relayfs_fs) + +EXPORT_SYMBOL_GPL(relayfs_open); +EXPORT_SYMBOL_GPL(relayfs_poll); +EXPORT_SYMBOL_GPL(relayfs_mmap); +EXPORT_SYMBOL_GPL(relayfs_release); +EXPORT_SYMBOL_GPL(relayfs_file_operations); +EXPORT_SYMBOL_GPL(relayfs_create_dir); +EXPORT_SYMBOL_GPL(relayfs_remove_dir); + +MODULE_AUTHOR("Tom Zanussi <zanussi@us.ibm.com> and Karim Yaghmour <karim@opersys.com>"); +MODULE_DESCRIPTION("Relay Filesystem"); +MODULE_LICENSE("GPL"); + diff --git a/runtime/relayfs/linux/relayfs_fs.h b/runtime/relayfs/linux/relayfs_fs.h new file mode 100644 index 00000000..1f697c3b --- /dev/null +++ b/runtime/relayfs/linux/relayfs_fs.h @@ -0,0 +1,263 @@ +/* + * linux/include/linux/relayfs_fs.h + * + * Copyright (C) 2002, 2003 - Tom Zanussi (zanussi@us.ibm.com), IBM Corp + * Copyright (C) 1999, 2000, 2001, 2002 - Karim Yaghmour (karim@opersys.com) + * + * RelayFS definitions and declarations + */ + +#ifndef _LINUX_RELAYFS_FS_H +#define _LINUX_RELAYFS_FS_H + +#include <linux/config.h> +#include <linux/types.h> +#include <linux/sched.h> +#include <linux/wait.h> +#include <linux/list.h> +#include <linux/fs.h> +#include <linux/poll.h> +#include <linux/kref.h> + +/* + * Tracks changes to rchan_buf struct + */ +#define RELAYFS_CHANNEL_VERSION 3 + +/* + * Per-cpu relay channel buffer + */ +struct rchan_buf +{ + void *start; /* start of channel buffer */ + void *data; /* start of current sub-buffer */ + unsigned offset; /* current offset into sub-buffer */ + atomic_t subbufs_produced; /* count of sub-buffers produced */ + atomic_t subbufs_consumed; /* count of sub-buffers consumed */ + atomic_t unfull; /* state has gone from full to not */ + struct rchan *chan; /* associated channel */ + wait_queue_head_t read_wait; /* reader wait queue */ + struct work_struct wake_readers; /* reader wake-up work struct */ + struct dentry *dentry; /* channel file dentry */ + struct kref kref; /* channel buffer refcount */ + struct page **page_array; /* array of current buffer pages */ + int page_count; /* number of current buffer pages */ + unsigned *padding; /* padding counts per sub-buffer */ + unsigned *commit; /* commit counts per sub-buffer */ + int finalized; /* buffer has been finalized */ +} ____cacheline_aligned; + +/* + * Relay channel data structure + */ +struct rchan +{ + u32 version; /* the version of this struct */ + unsigned subbuf_size; /* sub-buffer size */ + unsigned n_subbufs; /* number of sub-buffers per buffer */ + unsigned alloc_size; /* total buffer size allocated */ + int overwrite; /* overwrite buffer when full? */ + struct rchan_callbacks *cb; /* client callbacks */ + struct kref kref; /* channel refcount */ + struct rchan_buf *buf[NR_CPUS]; /* per-cpu channel buffers */ +}; + +/* + * Relayfs inode + */ +struct relayfs_inode_info +{ + struct inode vfs_inode; + struct rchan_buf *buf; +}; + +static inline struct relayfs_inode_info *RELAYFS_I(struct inode *inode) +{ + return container_of(inode, struct relayfs_inode_info, vfs_inode); +} + +/* + * Relay channel client callbacks + */ +struct rchan_callbacks +{ + /* + * subbuf_start - called on buffer-switch to a new sub-buffer + * @buf: the channel buffer containing the new sub-buffer + * @subbuf: the start of the new sub-buffer + * @prev_subbuf_idx: the previous sub-buffer's index + * @prev_subbuf: the start of the previous sub-buffer + * + * NOTE: subbuf_start will also be invoked when the buffer is + * created, so that the first sub-buffer can be initialized + * if necessary. In this case, prev_subbuf will be NULL. + */ + int (*subbuf_start) (struct rchan_buf *buf, + void *subbuf, + unsigned prev_subbuf_idx, + void *prev_subbuf); + + /* + * deliver - deliver a guaranteed full sub-buffer to client + * @buf: the channel buffer containing the sub-buffer + * @subbuf_idx: the sub-buffer's index + * @subbuf: the start of the new sub-buffer + * + * Only works if relay_commit is also used + */ + void (*deliver) (struct rchan_buf *buf, + unsigned subbuf_idx, + void *subbuf); + + /* + * buf_mapped - relayfs buffer mmap notification + * @buf: the channel buffer + * @filp: relayfs file pointer + * + * Called when a relayfs file is successfully mmapped + */ + void (*buf_mapped)(struct rchan_buf *buf, + struct file *filp); + + /* + * buf_unmapped - relayfs buffer unmap notification + * @buf: the channel buffer + * @filp: relayfs file pointer + * + * Called when a relayfs file is successfully unmapped + */ + void (*buf_unmapped)(struct rchan_buf *buf, + struct file *filp); + + /* + * buf_full - relayfs buffer full notification + * @buf: the channel channel buffer + * @subbuf_idx: the current sub-buffer's index + * @subbuf: the start of the current sub-buffer + * + * Called when a relayfs buffer becomes full + */ + void (*buf_full)(struct rchan_buf *buf, + unsigned subbuf_idx, + void *subbuf); +}; + +/* + * relayfs kernel API, fs/relayfs/relay.c + */ + +struct rchan *relay_open(const char *base_filename, + struct dentry *parent, + unsigned subbuf_size, + unsigned n_subbufs, + int overwrite, + struct rchan_callbacks *cb); +extern void relay_close(struct rchan *chan); +extern void relay_flush(struct rchan *chan); +extern void relay_subbufs_consumed(struct rchan *chan, + int cpu, + int subbufs_consumed); +extern void relay_reset(struct rchan *chan); +extern unsigned relay_switch_subbuf(struct rchan_buf *buf, + unsigned length); +extern void relay_commit(struct rchan_buf *buf, + void *reserved, + unsigned count); +extern struct dentry *relayfs_create_dir(const char *name, + struct dentry *parent); +extern int relayfs_remove_dir(struct dentry *dentry); + +/** + * relay_write - write data into the channel + * @chan: relay channel + * @data: data to be written + * @length: number of bytes to write + * + * Writes data into the current cpu's channel buffer. + * + * Protects the buffer by disabling interrupts. Use this + * if you might be logging from interrupt context. Try + * __relay_write() if you know you won't be logging from + * interrupt context. + */ +static inline void relay_write(struct rchan *chan, + const void *data, + unsigned length) +{ + unsigned long flags; + struct rchan_buf *buf; + + local_irq_save(flags); + buf = chan->buf[smp_processor_id()]; + if (unlikely(buf->offset + length > chan->subbuf_size)) + length = relay_switch_subbuf(buf, length); + memcpy(buf->data + buf->offset, data, length); + buf->offset += length; + local_irq_restore(flags); +} + +/** + * __relay_write - write data into the channel + * @chan: relay channel + * @data: data to be written + * @length: number of bytes to write + * + * Writes data into the current cpu's channel buffer. + * + * Protects the buffer by disabling preemption. Use + * relay_write() if you might be logging from interrupt + * context. + */ +static inline void __relay_write(struct rchan *chan, + const void *data, + unsigned length) +{ + struct rchan_buf *buf; + + buf = chan->buf[get_cpu()]; + if (unlikely(buf->offset + length > buf->chan->subbuf_size)) + length = relay_switch_subbuf(buf, length); + memcpy(buf->data + buf->offset, data, length); + buf->offset += length; + put_cpu(); +} + +/** + * relay_reserve - reserve slot in channel buffer + * @chan: relay channel + * @length: number of bytes to reserve + * + * Returns pointer to reserved slot, NULL if full. + * + * Reserves a slot in the current cpu's channel buffer. + * Does not protect the buffer at all - caller must provide + * appropriate synchronization. + */ +static inline void *relay_reserve(struct rchan *chan, unsigned length) +{ + void *reserved; + struct rchan_buf *buf = chan->buf[smp_processor_id()]; + + if (unlikely(buf->offset + length > buf->chan->subbuf_size)) { + length = relay_switch_subbuf(buf, length); + if (!length) + return NULL; + } + reserved = buf->data + buf->offset; + buf->offset += length; + + return reserved; +} + +/* + * exported relayfs file operations, fs/relayfs/inode.c + */ + +extern struct file_operations relayfs_file_operations; +extern int relayfs_open(struct inode *inode, struct file *filp); +extern unsigned int relayfs_poll(struct file *filp, poll_table *wait); +extern int relayfs_mmap(struct file *filp, struct vm_area_struct *vma); +extern int relayfs_release(struct inode *inode, struct file *filp); + +#endif /* _LINUX_RELAYFS_FS_H */ + diff --git a/runtime/relayfs/relay.c b/runtime/relayfs/relay.c new file mode 100644 index 00000000..82ad71c7 --- /dev/null +++ b/runtime/relayfs/relay.c @@ -0,0 +1,530 @@ +/* + * Public API and common code for RelayFS. + * + * See Documentation/filesystems/relayfs.txt for an overview of relayfs. + * + * Copyright (C) 2002-2005 - Tom Zanussi (zanussi@us.ibm.com), IBM Corp + * Copyright (C) 1999-2005 - Karim Yaghmour (karim@opersys.com) + * + * This file is released under the GPL. + */ + +#include <linux/errno.h> +#include <linux/stddef.h> +#include <linux/slab.h> +#include <linux/module.h> +#include <linux/string.h> +#include <linux/relayfs_fs.h> +#include "relay.h" +#include "buffers.h" + +/** + * relay_buf_empty - boolean, is the channel buffer empty? + * @buf: channel buffer + * + * Returns 1 if the buffer is empty, 0 otherwise. + */ +int relay_buf_empty(struct rchan_buf *buf) +{ + int produced = atomic_read(&buf->subbufs_produced); + int consumed = atomic_read(&buf->subbufs_consumed); + + return (produced - consumed) ? 0 : 1; +} + +/** + * relay_buf_full - boolean, is the channel buffer full? + * @buf: channel buffer + * + * Returns 1 if the buffer is full, 0 otherwise. + */ +static inline int relay_buf_full(struct rchan_buf *buf) +{ + int produced, consumed; + + if (buf->chan->overwrite) + return 0; + + produced = atomic_read(&buf->subbufs_produced); + consumed = atomic_read(&buf->subbufs_consumed); + + return (produced - consumed > buf->chan->n_subbufs - 1) ? 1 : 0; +} + +/* + * High-level relayfs kernel API and associated functions. + */ + +/* + * rchan_callback implementations defining default channel behavior. Used + * in place of corresponding NULL values in client callback struct. + */ + +/* + * subbuf_start() default callback. Does nothing. + */ +static int subbuf_start_default_callback (struct rchan_buf *buf, + void *subbuf, + unsigned prev_subbuf_idx, + void *prev_subbuf) +{ + return 0; +} + +/* + * deliver() default callback. Does nothing. + */ +static void deliver_default_callback (struct rchan_buf *buf, + unsigned subbuf_idx, + void *subbuf) +{ +} + +/* + * buf_mapped() default callback. Does nothing. + */ +static void buf_mapped_default_callback(struct rchan_buf *buf, + struct file *filp) +{ +} + +/* + * buf_unmapped() default callback. Does nothing. + */ +static void buf_unmapped_default_callback(struct rchan_buf *buf, + struct file *filp) +{ +} + +/* + * buf_full() default callback. Does nothing. + */ +static void buf_full_default_callback(struct rchan_buf *buf, + unsigned subbuf_idx, + void *subbuf) +{ +} + +/* relay channel default callbacks */ +static struct rchan_callbacks default_channel_callbacks = { + .subbuf_start = subbuf_start_default_callback, + .deliver = deliver_default_callback, + .buf_mapped = buf_mapped_default_callback, + .buf_unmapped = buf_unmapped_default_callback, + .buf_full = buf_full_default_callback, +}; + +/** + * wakeup_readers - wake up readers waiting on a channel + * @private: the channel buffer + * + * This is the work function used to defer reader waking. The + * reason waking is deferred is that calling directly from write + * causes problems if you're writing from say the scheduler. + */ +static void wakeup_readers(void *private) +{ + struct rchan_buf *buf = private; + wake_up_interruptible(&buf->read_wait); +} + +/** + * get_next_subbuf - return next sub-buffer within channel buffer + * @buf: channel buffer + */ +static inline void *get_next_subbuf(struct rchan_buf *buf) +{ + void *next = buf->data + buf->chan->subbuf_size; + if (next >= buf->start + buf->chan->subbuf_size * buf->chan->n_subbufs) + next = buf->start; + + return next; +} + +/** + * __relay_reset - reset a channel buffer + * @buf: the channel buffer + * @init: 1 if this is a first-time initialization + * + * See relay_reset for description of effect. + */ +static inline void __relay_reset(struct rchan_buf *buf, int init) +{ + int i; + + if (init) { + init_waitqueue_head(&buf->read_wait); + kref_init(&buf->kref); + } + + atomic_set(&buf->subbufs_produced, 0); + atomic_set(&buf->subbufs_consumed, 0); + atomic_set(&buf->unfull, 0); + buf->finalized = 0; + buf->data = buf->start; + buf->offset = 0; + + for (i = 0; i < buf->chan->n_subbufs; i++) { + buf->padding[i] = 0; + buf->commit[i] = 0; + } + + buf->offset = buf->chan->cb->subbuf_start(buf, buf->data, 0, NULL); + buf->commit[0] = buf->offset; + + INIT_WORK(&buf->wake_readers, NULL, NULL); +} + +/** + * relay_reset - reset the channel + * @chan: the channel + * + * Returns 0 if successful, negative if not. + * + * This has the effect of erasing all data from all channel buffers + * and restarting the channel in its initial state. The buffers + * are not freed, so any mappings are still in effect. + * + * NOTE: Care should be taken that the channel isn't actually + * being used by anything when this call is made. + */ +void relay_reset(struct rchan *chan) +{ + int i; + + if (!chan) + return; + + for (i = 0; i < NR_CPUS; i++) { + if (!chan->buf[i]) + continue; + __relay_reset(chan->buf[i], 0); + } +} + +/** + * relay_open_buf - create a new channel buffer in relayfs + * + * Internal - used by relay_open(). + */ +static struct rchan_buf *relay_open_buf(struct rchan *chan, + const char *filename, + struct dentry *parent) +{ + struct rchan_buf *buf; + struct dentry *dentry; + + /* Create file in fs */ + dentry = relayfs_create_file(filename, parent, S_IRUSR, chan); + if (!dentry) + return NULL; + + buf = RELAYFS_I(dentry->d_inode)->buf; + buf->dentry = dentry; + __relay_reset(buf, 1); + + return buf; +} + +/** + * relay_close_buf - close a channel buffer + * @buf: channel buffer + * + * Marks the buffer finalized and restores the default callbacks. + * The channel buffer and channel buffer data structure are then freed + * automatically when the last reference is given up. + */ +static inline void relay_close_buf(struct rchan_buf *buf) +{ + buf->finalized = 1; + buf->chan->cb = &default_channel_callbacks; + kref_put(&buf->kref, relay_remove_buf); +} + +static inline void setup_callbacks(struct rchan *chan, + struct rchan_callbacks *cb) +{ + if (!cb) { + chan->cb = &default_channel_callbacks; + return; + } + + if (!cb->subbuf_start) + cb->subbuf_start = subbuf_start_default_callback; + if (!cb->deliver) + cb->deliver = deliver_default_callback; + if (!cb->buf_mapped) + cb->buf_mapped = buf_mapped_default_callback; + if (!cb->buf_unmapped) + cb->buf_unmapped = buf_unmapped_default_callback; + if (!cb->buf_full) + cb->buf_full = buf_full_default_callback; + chan->cb = cb; +} + +/** + * relay_open - create a new relayfs channel + * @base_filename: base name of files to create + * @parent: dentry of parent directory, NULL for root directory + * @subbuf_size: size of sub-buffers + * @n_subbufs: number of sub-buffers + * @overwrite: overwrite buffer when full? + * @cb: client callback functions + * + * Returns channel pointer if successful, NULL otherwise. + * + * Creates a channel buffer for each cpu using the sizes and + * attributes specified. The created channel buffer files + * will be named base_filename0...base_filenameN-1. File + * permissions will be S_IRUSR. + */ +struct rchan *relay_open(const char *base_filename, + struct dentry *parent, + unsigned subbuf_size, + unsigned n_subbufs, + int overwrite, + struct rchan_callbacks *cb) +{ + int i; + struct rchan *chan; + char *tmpname; + + if (!base_filename) + return NULL; + + if (!(subbuf_size && n_subbufs)) + return NULL; + + chan = kcalloc(1, sizeof(struct rchan), GFP_KERNEL); + if (!chan) + return NULL; + + chan->version = RELAYFS_CHANNEL_VERSION; + chan->overwrite = overwrite; + chan->n_subbufs = n_subbufs; + chan->subbuf_size = subbuf_size; + chan->alloc_size = FIX_SIZE(subbuf_size * n_subbufs); + setup_callbacks(chan, cb); + kref_init(&chan->kref); + + tmpname = kmalloc(NAME_MAX + 1, GFP_KERNEL); + if (!tmpname) + goto free_chan; + + for_each_online_cpu(i) { + sprintf(tmpname, "%s%d", base_filename, i); + chan->buf[i] = relay_open_buf(chan, tmpname, parent); + if (!chan->buf[i]) + goto free_bufs; + } + + kfree(tmpname); + return chan; + +free_bufs: + for (i = 0; i < NR_CPUS; i++) { + if (!chan->buf[i]) + break; + relay_close_buf(chan->buf[i]); + } + kfree(tmpname); + +free_chan: + kref_put(&chan->kref, relay_destroy_channel); + return NULL; +} + +/** + * deliver_check - deliver a guaranteed full sub-buffer if applicable + */ +static inline void deliver_check(struct rchan_buf *buf, + unsigned subbuf_idx) +{ + void *subbuf; + unsigned full = buf->chan->subbuf_size - buf->padding[subbuf_idx]; + + if (buf->commit[subbuf_idx] == full) { + subbuf = buf->start + subbuf_idx * buf->chan->subbuf_size; + buf->chan->cb->deliver(buf, subbuf_idx, subbuf); + } +} + +/** + * do_switch - change subbuf pointer and do related bookkeeping + */ +static inline void do_switch(struct rchan_buf *buf, unsigned new, unsigned old) +{ + unsigned start = 0; + void *old_data = buf->start + old * buf->chan->subbuf_size; + + buf->data = get_next_subbuf(buf); + buf->padding[new] = 0; + start = buf->chan->cb->subbuf_start(buf, buf->data, old, old_data); + buf->offset = buf->commit[new] = start; +} + +/** + * relay_switch_subbuf - switch to a new sub-buffer + * @buf: channel buffer + * @length: size of current event + * + * Returns either the length passed in or 0 if full. + + * Performs sub-buffer-switch tasks such as invoking callbacks, + * updating padding counts, waking up readers, etc. + */ +unsigned relay_switch_subbuf(struct rchan_buf *buf, unsigned length) +{ + int new, old, produced = atomic_read(&buf->subbufs_produced); + unsigned padding; + + if (atomic_read(&buf->unfull)) { + atomic_set(&buf->unfull, 0); + new = produced % buf->chan->n_subbufs; + old = (produced - 1) % buf->chan->n_subbufs; + do_switch(buf, new, old); + return 0; + } + + if (unlikely(relay_buf_full(buf))) + return 0; + + old = produced % buf->chan->n_subbufs; + padding = buf->chan->subbuf_size - buf->offset; + buf->padding[old] = padding; + deliver_check(buf, old); + buf->offset = buf->chan->subbuf_size; + atomic_inc(&buf->subbufs_produced); + + if (waitqueue_active(&buf->read_wait)) { + PREPARE_WORK(&buf->wake_readers, wakeup_readers, buf); + schedule_delayed_work(&buf->wake_readers, 1); + } + + if (unlikely(relay_buf_full(buf))) { + void *old_data = buf->start + old * buf->chan->subbuf_size; + buf->chan->cb->buf_full(buf, old, old_data); + return 0; + } + + new = (produced + 1) % buf->chan->n_subbufs; + do_switch(buf, new, old); + + return length; +} + +/** + * relay_commit - add count bytes to a sub-buffer's commit count + * @buf: channel buffer + * @reserved: reserved address associated with commit + * @count: number of bytes committed + * + * Invokes deliver() callback if sub-buffer is completely written. + */ +void relay_commit(struct rchan_buf *buf, + void *reserved, + unsigned count) +{ + unsigned offset, subbuf_idx; + + offset = reserved - buf->start; + subbuf_idx = offset / buf->chan->subbuf_size; + buf->commit[subbuf_idx] += count; + deliver_check(buf, subbuf_idx); +} + +/** + * relay_subbufs_consumed - update the buffer's sub-buffers-consumed count + * @chan: the channel + * @cpu: the cpu associated with the channel buffer to update + * @subbufs_consumed: number of sub-buffers to add to current buf's count + * + * Adds to the channel buffer's consumed sub-buffer count. + * subbufs_consumed should be the number of sub-buffers newly consumed, + * not the total consumed. + * + * NOTE: kernel clients don't need to call this function if the channel + * mode is 'overwrite'. + */ +void relay_subbufs_consumed(struct rchan *chan, int cpu, int subbufs_consumed) +{ + int produced, consumed; + struct rchan_buf *buf; + + if (!chan) + return; + + if (cpu >= NR_CPUS || !chan->buf[cpu]) + return; + + buf = chan->buf[cpu]; + if (relay_buf_full(buf)) + atomic_set(&buf->unfull, 1); + + atomic_add(subbufs_consumed, &buf->subbufs_consumed); + produced = atomic_read(&buf->subbufs_produced); + consumed = atomic_read(&buf->subbufs_consumed); + if (consumed > produced) + atomic_set(&buf->subbufs_consumed, produced); +} + +/** + * relay_destroy_channel - free the channel struct + * + * Should only be called from kref_put(). + */ +void relay_destroy_channel(struct kref *kref) +{ + struct rchan *chan = container_of(kref, struct rchan, kref); + kfree(chan); +} + +/** + * relay_close - close the channel + * @chan: the channel + * + * Closes all channel buffers and frees the channel. + */ +void relay_close(struct rchan *chan) +{ + int i; + + if (!chan) + return; + + for (i = 0; i < NR_CPUS; i++) { + if (!chan->buf[i]) + continue; + relay_close_buf(chan->buf[i]); + } + + kref_put(&chan->kref, relay_destroy_channel); +} + +/** + * relay_flush - close the channel + * @chan: the channel + * + * Flushes all channel buffers i.e. forces buffer switch. + */ +void relay_flush(struct rchan *chan) +{ + int i; + + if (!chan) + return; + + for (i = 0; i < NR_CPUS; i++) { + if (!chan->buf[i]) + continue; + relay_switch_subbuf(chan->buf[i], 0); + } +} + +EXPORT_SYMBOL_GPL(relay_open); +EXPORT_SYMBOL_GPL(relay_close); +EXPORT_SYMBOL_GPL(relay_flush); +EXPORT_SYMBOL_GPL(relay_reset); +EXPORT_SYMBOL_GPL(relay_subbufs_consumed); +EXPORT_SYMBOL_GPL(relay_commit); +EXPORT_SYMBOL_GPL(relay_switch_subbuf); diff --git a/runtime/relayfs/relay.h b/runtime/relayfs/relay.h new file mode 100644 index 00000000..703503fa --- /dev/null +++ b/runtime/relayfs/relay.h @@ -0,0 +1,12 @@ +#ifndef _RELAY_H +#define _RELAY_H + +struct dentry *relayfs_create_file(const char *name, + struct dentry *parent, + int mode, + struct rchan *chan); +extern int relayfs_remove(struct dentry *dentry); +extern int relay_buf_empty(struct rchan_buf *buf); +extern void relay_destroy_channel(struct kref *kref); + +#endif /* _RELAY_H */ diff --git a/runtime/relayfs/relayfs.txt b/runtime/relayfs/relayfs.txt new file mode 100644 index 00000000..ada829bb --- /dev/null +++ b/runtime/relayfs/relayfs.txt @@ -0,0 +1,206 @@ + +relayfs - a high-speed data relay filesystem +============================================ + +relayfs is a filesystem designed to provide an efficient mechanism for +tools and facilities to relay large and potentially sustained streams +of data from kernel space to user space. + +The main abstraction of relayfs is the 'channel'. A channel consists +of a set of per-cpu kernel buffers each represented by a file in the +relayfs filesystem. Kernel clients write into a channel using +efficient write functions which automatically log to the current cpu's +channel buffer. User space applications mmap() the per-cpu files and +retrieve the data as it becomes available. + +The format of the data logged into the channel buffers is completely +up to the relayfs client; relayfs does however provide hooks which +allow clients to impose some stucture on the buffer data. Nor does +relayfs implement any form of data filtering - this also is left to +the client. The purpose is to keep relayfs as simple as possible. + +This document provides an overview of the relayfs API. The details of +the function parameters are documented along with the functions in the +filesystem code - please see that for details. + + +The relayfs user space API +========================== + +relayfs implements basic file operations for user space access to +relayfs channel buffer data. Here are the file operations that are +available and some comments regarding their behavior: + +open() enables user to open an _existing_ buffer. + +mmap() results in channel buffer being mapped into the caller's + memory space. + +poll() POLLIN/POLLRDNORM/POLLERR supported. User applications are + notified when sub-buffer boundaries are crossed. + +close() decrements the channel buffer's refcount. When the refcount + reaches 0 i.e. when no process or kernel client has the buffer + open, the channel buffer is freed. + + +In order for a user application to make use of relayfs files, the +relayfs filesystem must be mounted. For example, + + mount -t relayfs relayfs /mnt/relay + +NOTE: relayfs doesn't need to be mounted for kernel clients to create + or use channels - it only needs to be mounted when user space + applications need access to the buffer data. + + +The relayfs kernel API +====================== + +Here's a summary of the API relayfs provides to in-kernel clients: + + + channel management functions: + + relay_open(base_filename, parent, subbuf_size, n_subbufs, + overwrite, callbacks) + relay_close(chan) + relay_flush(chan) + relay_reset(chan) + relayfs_create_dir(name, parent) + relayfs_remove_dir(dentry) + relay_commit(buf, reserved, count) + relay_subbufs_consumed(chan, cpu, subbufs_consumed) + + write functions: + + relay_write(chan, data, length) + __relay_write(chan, data, length) + relay_reserve(chan, length) + + callbacks: + + subbuf_start(buf, subbuf, prev_subbuf_idx, prev_subbuf) + deliver(buf, subbuf_idx, subbuf) + buf_mapped(buf, filp) + buf_unmapped(buf, filp) + buf_full(buf, subbuf_idx) + + +A relayfs channel is made of up one or more per-cpu channel buffers, +each implemented as a circular buffer subdivided into one or more +sub-buffers. + +relay_open() is used to create a channel, along with its per-cpu +channel buffers. Each channel buffer will have an associated file +created for it in the relayfs filesystem, which can be opened and +mmapped from user space if desired. The files are named +basename0...basenameN-1 where N is the number of online cpus, and by +default will be created in the root of the filesystem. If you want a +directory structure to contain your relayfs files, you can create it +with relayfs_create_dir() and pass the parent directory to +relay_open(). Clients are responsible for cleaning up any directory +structure they create when the channel is closed - use +relayfs_remove_dir() for that. + +The total size of each per-cpu buffer is calculated by multiplying the +number of sub-buffers by the sub-buffer size passed into relay_open(). +The idea behind sub-buffers is that they're basically an extension of +double-buffering to N buffers, and they also allow applications to +easily implement random-access-on-buffer-boundary schemes, which can +be important for some high-volume applications. The number and size +of sub-buffers is completely dependent on the application and even for +the same application, different conditions will warrant different +values for these parameters at different times. Typically, the right +values to use are best decided after some experimentation; in general, +though, it's safe to assume that having only 1 sub-buffer is a bad +idea - you're guaranteed to either overwrite data or lose events +depending on the channel mode being used. + +relayfs channels can be opened in either of two modes - 'overwrite' or +'no-overwrite'. In overwrite mode, writes continuously cycle around +the buffer and will never fail, but will unconditionally overwrite old +data regardless of whether it's actually been consumed. In +no-overwrite mode, writes will fail i.e. data will be lost, if the +number of unconsumed sub-buffers equals the total number of +sub-buffers in the channel. In this mode, the client is reponsible +for notifying relayfs when sub-buffers have been consumed via +relay_subbufs_consumed(). A full buffer will become 'unfull' and +logging will continue once the client calls relay_subbufs_consumed() +again. When a buffer becomes full, the buf_full() callback is invoked +to notify the client. In both modes, the subbuf_start() callback will +notify the client whenever a sub-buffer boundary is crossed. This can +be used to write header information into the new sub-buffer or fill in +header information reserved in the previous sub-buffer. One piece of +information that's useful to save in a reserved header slot is the +number of bytes of 'padding' for a sub-buffer, which is the amount of +unused space at the end of a sub-buffer. The padding count for each +sub-buffer is contained in an array in the rchan_buf struct passed +into the subbuf_start() callback: rchan_buf->padding[prev_subbuf_idx] +can be used to to get the padding for the just-finished sub-buffer. +subbuf_start() is also called for the first sub-buffer in each channel +buffer when the channel is created. The mode is specified to +relay_open() using the overwrite parameter. + +kernel clients write data into the current cpu's channel buffer using +relay_write() or __relay_write(). relay_write() is the main logging +function - it uses local_irqsave() to protect the buffer and should be +used if you might be logging from interrupt context. If you know +you'll never be logging from interrupt context, you can use +__relay_write(), which only disables preemption. These functions +don't return a value, so you can't determine whether or not they +failed - the assumption is that you wouldn't want to check a return +value in the fast logging path anyway, and that they'll always succeed +unless the buffer is full and in no-overwrite mode, in which case +you'll be notified via the buf_full() callback. + +relay_reserve() is used to reserve a slot in a channel buffer which +can be written to later. This would typically be used in applications +that need to write directly into a channel buffer without having to +stage data in a temporary buffer beforehand. Because the actual write +may not happen immediately after the slot is reserved, applications +using relay_reserve() can call relay_commit() to notify relayfs when +the slot has actually been written. When all the reserved slots have +been committed, the deliver() callback is invoked to notify the client +that a guaranteed full sub-buffer has been produced. Because the +write is under control of the client and is separated from the +reserve, relay_reserve() doesn't protect the buffer at all - it's up +to the client to provide the appropriate synchronization when using +relay_reserve(). + +The client calls relay_close() when it's finished using the channel. +The channel and its associated buffers are destroyed when there are no +longer any references to any of the channel buffers. relay_flush() +forces a sub-buffer switch on all the channel buffers, and can be used +to finalize and process the last sub-buffers before the channel is +closed. + +Some applications may want to keep a channel around and re-use it +rather than open and close a new channel for each use. relay_reset() +can be used for this purpose - it resets a channel to its initial +state without reallocating channel buffer memory or destroying +existing mappings. It should however only be called when it's safe to +do so i.e. when the channel isn't currently being written to. + +Finally, there are a couple of utility callbacks that can be used for +different purposes. buf_mapped() is called whenever a channel buffer +is mmapped from user space and buf_unmapped() is called when it's +unmapped. The client can use this notification to trigger actions +within the kernel application, such as enabling/disabling logging to +the channel. + + +Credits +======= + +The ideas and specs for relayfs came about as a result of discussions +on tracing involving the following: + +Michel Dagenais <michel.dagenais@polymtl.ca> +Richard Moore <richardj_moore@uk.ibm.com> +Bob Wisniewski <bob@watson.ibm.com> +Karim Yaghmour <karim@opersys.com> +Tom Zanussi <zanussi@us.ibm.com> + +Also thanks to Hubertus Franke for a lot of useful suggestions and bug +reports. |