[PATCH v4 4/4] xfs_io: Allow partial writes

[Goldwyn Rodrigues <rgoldwyn@suse.de>]

From: Goldwyn Rodrigues <rgoldwyn@suse.com>

Partial writes are performed when there is an error midway
while performing the I/O. Perform the write exactly once and
return the number of bytes written so far, until the error.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
---
 io/io.h           |  1 +
 io/pwrite.c       | 25 ++++++++++++++++++++++++-
 man/man8/xfs_io.8 |  3 +++
 3 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/io/io.h b/io/io.h
index 6a0fe657..3862985f 100644
--- a/io/io.h
+++ b/io/io.h
@@ -25,6 +25,7 @@
 #define IO_RANDOM	( 0)
 #define IO_FORWARD	( 1)
 #define IO_BACKWARD	(-1)
+#define IO_ONCE		( 2)
 
 /*
  * File descriptor options
diff --git a/io/pwrite.c b/io/pwrite.c
index c218f686..b77c0975 100644
--- a/io/pwrite.c
+++ b/io/pwrite.c
@@ -47,6 +47,7 @@ pwrite_help(void)
 " -W   -- call fsync(2) at the end (included in timing results)\n"
 " -B   -- write backwards through the range from offset (backwards N bytes)\n"
 " -F   -- write forwards through the range of bytes from offset (default)\n"
+" -O   -- perform pwrite call once and return (maybe partial) bytes written\n"
 " -R   -- write at random offsets in the specified range of bytes\n"
 " -Z N -- zeed the random number generator (used when writing randomly)\n"
 "         (heh, zorry, the -s/-S arguments were already in use in pwrite)\n"
@@ -261,6 +262,22 @@ write_buffer(
 	return ops;
 }
 
+static int
+write_once(
+	off64_t		offset,
+	long long	count,
+	long long	*total,
+	int		pwritev2_flags)
+{
+	size_t bytes;
+	bytes = do_pwrite(file->fd, offset, count, count, pwritev2_flags);
+	if (bytes < 0)
+		return -1;
+	*total = bytes;
+	return 1;
+}
+
+
 static int
 pwrite_f(
 	int		argc,
@@ -282,7 +299,7 @@ pwrite_f(
 	init_cvtnum(&fsblocksize, &fssectsize);
 	bsize = fsblocksize;
 
-	while ((c = getopt(argc, argv, "b:BCdf:Fi:NqRs:S:uV:wWZ:")) != EOF) {
+	while ((c = getopt(argc, argv, "b:BCdf:Fi:NqRs:OS:uV:wWZ:")) != EOF) {
 		switch (c) {
 		case 'b':
 			tmp = cvtnum(fsblocksize, fssectsize, optarg);
@@ -304,6 +321,9 @@ pwrite_f(
 		case 'R':
 			direction = IO_RANDOM;
 			break;
+		case 'O':
+			direction = IO_ONCE;
+			break;
 		case 'd':
 			dflag = 1;
 			break;
@@ -401,6 +421,9 @@ pwrite_f(
 	case IO_BACKWARD:
 		c = write_backward(offset, &count, &total, pwritev2_flags);
 		break;
+	case IO_ONCE:
+		c = write_once(offset, count, &total, pwritev2_flags);
+		break;
 	default:
 		total = 0;
 		ASSERT(0);
diff --git a/man/man8/xfs_io.8 b/man/man8/xfs_io.8
index 5c0565ec..ff48689d 100644
--- a/man/man8/xfs_io.8
+++ b/man/man8/xfs_io.8
@@ -263,6 +263,9 @@ write the buffers in a reserve sequential direction.
 .B \-R
 write the buffers in the give range in a random order.
 .TP
+.B \-O
+perform pwrite once and return the (maybe partial) bytes written.
+.TP
 .B \-Z seed
 specify the random number seed used for random write
 .TP
-- 
2.14.2