nfs-utils: Increase the stdio file buffer size for procfs files

Previously, when writing to /proc/net/rpc/*/channel, if a cache line
were larger than the default buffer size (likely 1024 bytes), mountd
and svcgssd would split writes into a number of buffer-sized writes.
Each of these writes would get an EINVAL error back from the kernel
procfs handle (it expects line-oriented input and does not account for
multiple/split writes), and no cache update would occur.

When such behavior occurs, NFS clients depending on mountd to finish
the cache operation would block/hang, or receive EPERM, depending on
the context of the operation.  This is likely to happen if a user is a
member of a large (~100-200) number of groups.

Instead, every fopen() on the procfs files in question is followed by
a call to setvbuf(), using a per-file dedicated buffer of
RPC_CHAN_BUF_SIZE length.

Really, mountd should not be using stdio-style buffered file operations
on files in /proc to begin with.  A better solution would be to use
internally managed buffers and calls to write() instead of these stdio
calls, but that would be a more extensive change; so this is proposed
as a quick and not-so-dirty fix in the meantime.

Signed-off-by: Sean Finney <sean.finney@sonyericsson.com>
Signed-off-by: Steve Dickson <steved@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/utils/gssd/svcgssd_proc.c b/utils/gssd/svcgssd_proc.c
index 7a916d7..c714d99 100644
--- a/utils/gssd/svcgssd_proc.c
+++ b/utils/gssd/svcgssd_proc.c
@@ -56,6 +56,7 @@
 #include "gss_util.h"
 #include "err_util.h"
 #include "context.h"
+#include "misc.h"
 #include "gss_oids.h"
 #include "svcgssd_krb5.h"
 
@@ -71,6 +72,7 @@ struct svc_cred {
 	int	cr_ngroups;
 	gid_t	cr_groups[NGROUPS];
 };
+static char vbuf[RPC_CHAN_BUF_SIZE];
 
 static int
 do_svc_downcall(gss_buffer_desc *out_handle, struct svc_cred *cred,
@@ -92,6 +94,7 @@ do_svc_downcall(gss_buffer_desc *out_handle, struct svc_cred *cred,
 			     SVCGSSD_CONTEXT_CHANNEL, strerror(errno));
 		goto out_err;
 	}
+	setvbuf(f, vbuf, _IOLBF, RPC_CHAN_BUF_SIZE);
 	qword_printhex(f, out_handle->value, out_handle->length);
 	/* XXX are types OK for the rest of this? */
 	/* For context cache, use the actual context endtime */