From 075df914c0355e1dcafad1a128877be11241725c Mon Sep 17 00:00:00 2001
From: Ondrej Kos <okos@redhat.com>
Date: Thu, 7 Feb 2013 12:11:43 +0100
Subject: UTIL: Add function for atomic I/O

---
 Makefile.am          |  2 ++
 src/util/atomic_io.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/util/atomic_io.h | 40 +++++++++++++++++++++++++++++++++++
 src/util/util.h      |  1 +
 4 files changed, 103 insertions(+)
 create mode 100644 src/util/atomic_io.c
 create mode 100644 src/util/atomic_io.h

diff --git a/Makefile.am b/Makefile.am
index e00b7ca5c..d668acc25 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -237,6 +237,7 @@ SSSD_UTIL_OBJ = \
     src/util/backup_file.c \
     src/util/strtonum.c \
     src/util/check_and_open.c \
+    src/util/atomic_io.c \
     src/util/refcount.c \
     $(SSSD_DEBUG_OBJ)
 
@@ -321,6 +322,7 @@ endif
 
 dist_noinst_HEADERS = \
     src/monitor/monitor.h \
+    src/util/atomic_io.h \
     src/util/crypto/sss_crypto.h \
     src/util/dlinklist.h \
     src/util/util.h \
diff --git a/src/util/atomic_io.c b/src/util/atomic_io.c
new file mode 100644
index 000000000..1543af9a0
--- /dev/null
+++ b/src/util/atomic_io.c
@@ -0,0 +1,60 @@
+/*
+    Authors:
+        Jan Cholasta <jcholast@redhat.com>
+
+    Copyright (C) 2012 Red Hat
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "util/atomic_io.h"
+
+/* based on code from libssh <http://www.libssh.org> */
+ssize_t sss_atomic_io_s(int fd, void *buf, size_t n, bool do_read)
+{
+    char *b = buf;
+    size_t pos = 0;
+    ssize_t res;
+    struct pollfd pfd;
+
+    pfd.fd = fd;
+    pfd.events = do_read ? POLLIN : POLLOUT;
+
+    while (n > pos) {
+        if (do_read) {
+            res = read(fd, b + pos, n - pos);
+        } else {
+            res = write(fd, b + pos, n - pos);
+        }
+        switch (res) {
+        case -1:
+            if (errno == EINTR) {
+                continue;
+            }
+            if (errno == EAGAIN || errno == EWOULDBLOCK) {
+                (void) poll(&pfd, 1, -1);
+                continue;
+            }
+            return -1;
+        case 0:
+            /* read returns 0 on end-of-file */
+            errno = do_read ? 0 : EPIPE;
+            return pos;
+        default:
+            pos += (size_t) res;
+        }
+    }
+
+    return pos;
+}
diff --git a/src/util/atomic_io.h b/src/util/atomic_io.h
new file mode 100644
index 000000000..ffae31d6c
--- /dev/null
+++ b/src/util/atomic_io.h
@@ -0,0 +1,40 @@
+/*
+    Authors:
+        Jan Cholasta <jcholast@redhat.com>
+
+    Copyright (C) 2012 Red Hat
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef __SSSD_ATOMIC_IO_H__
+#define __SSSD_ATOMIC_IO_H__
+
+#include <unistd.h>
+#include <stdbool.h>
+#include <poll.h>
+#include <errno.h>
+
+/* Performs a read or write operation in an manner that is seemingly atomic
+ * to the caller.
+ *
+ * Please note that the function does not perform any asynchronous operation
+ * so the operation might potentially block
+ */
+ssize_t sss_atomic_io_s(int fd, void *buf, size_t n, bool do_read);
+
+#define sss_atomic_read_s(fd, buf, n)  sss_atomic_io_s(fd, buf, n, true)
+#define sss_atomic_write_s(fd, buf, n) sss_atomic_io_s(fd, buf, n, false)
+
+#endif /* __SSSD_ATOMIC_IO_H__ */
diff --git a/src/util/util.h b/src/util/util.h
index 43fb007cb..43017aa0d 100644
--- a/src/util/util.h
+++ b/src/util/util.h
@@ -42,6 +42,7 @@
 #include <tevent.h>
 #include <ldb.h>
 #include <dhash.h>
+#include "util/atomic_io.h"
 
 #ifndef HAVE_ERRNO_T
 #define HAVE_ERRNO_T
-- 
cgit