lib: util: Add sys_pwrite_full().

A pwrite wrapper that will deal with EINTR and never return a short
write unless the file system returns an error. Copes with the
unspecified edge condition of pwrite returning zero by changing
the return to -1, errno = ENOSPC.

Thread-safe so may be used as a replacement for pwrite
inside pwrite_do() thread functions.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14361

Pair-Programmed-With: Stefan Metzmacher <metze@samba.org>

Signed-off-by: Jeremy Allison <jra@samba.org>
Signed-off-by: Stefan Metzmacher <metze@samba.org>

2 files changed, 50 insertions, 0 deletions

diff --git a/lib/util/sys_rw.c b/lib/util/sys_rw.c
index bfeb2e6b466..d74395fc409 100644
--- a/lib/util/sys_rw.c
+++ b/lib/util/sys_rw.c
@@ -204,3 +204,52 @@ ssize_t sys_pwrite(int fd, const void *buf, size_t count, off_t off)
 	} while (ret == -1 && errno == EINTR);
 	return ret;
 }
+
+/*******************************************************************
+ A pwrite wrapper that will deal with EINTR and never allow a short
+ write unless the file system returns an error.
+********************************************************************/
+
+ssize_t sys_pwrite_full(int fd, const void *buf, size_t count, off_t off)
+{
+	ssize_t total_written = 0;
+	const uint8_t *curr_buf = (const uint8_t *)buf;
+	size_t curr_count = count;
+	off_t curr_off = off;
+	bool ok;
+
+	ok = sys_valid_io_range(off, count);
+	if (!ok) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	while (curr_count != 0) {
+		ssize_t ret = sys_pwrite(fd,
+					 curr_buf,
+					 curr_count,
+					 curr_off);
+
+		if (ret == -1) {
+			return -1;
+		}
+		if (ret == 0) {
+			/* Ensure we can never spin. */
+			errno = ENOSPC;
+			return -1;
+		}
+
+		if (ret > curr_count) {
+			errno = EIO;
+			return -1;
+		}
+
+		curr_buf += ret;
+		curr_count -= ret;
+		curr_off += ret;
+
+		total_written += ret;
+	}
+
+	return total_written;
+}
diff --git a/lib/util/sys_rw.h b/lib/util/sys_rw.h
index 1e0dd3730a6..b224ecb30ac 100644
--- a/lib/util/sys_rw.h
+++ b/lib/util/sys_rw.h
@@ -36,5 +36,6 @@ ssize_t sys_writev(int fd, const struct iovec *iov, int iovcnt);
 ssize_t sys_pread(int fd, void *buf, size_t count, off_t off);
 ssize_t sys_pread_full(int fd, void *buf, size_t count, off_t off);
 ssize_t sys_pwrite(int fd, const void *buf, size_t count, off_t off);
+ssize_t sys_pwrite_full(int fd, const void *buf, size_t count, off_t off);
 
 #endif