posix: leverage FALLOC_FL_ZERO_RANGE in zerofill fop

Backport of http://review.gluster.org/#/c/15037/

posix_zerofill() implements zerofilling of a given (offset,length) by
doing a writev in a loop followed by an optional fsync on the file.
fallocate(2) has a FALLOC_FL_ZERO_RANGE flag which does away with all
this and provides the same result (from a userspace application point of
view) with a single syscall. This patch attempts the zerofill with the
latter and falls back to the former if it fails.

Tested using a libgfapi based C program on XFS and observed using gdb
that posix_zerofill()'s call to fallocate with FALLOC_FL_ZERO_RANGE was
a success.

Change-Id: Iceaf0cbc57c52dac63540872e8538d79e8dee631
BUG: 1361483
Signed-off-by: Ravishankar N <ravishankar@redhat.com>
Reviewed-on: http://review.gluster.org/15044
Smoke: Gluster Build System <jenkins@build.gluster.org>
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: Pranith Kumar Karampuri <pkarampu@redhat.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/xlators/storage/posix/src/posix.c b/xlators/storage/posix/src/posix.c
index a963f8a3b6b..bce074b4fd1 100644
--- a/xlators/storage/posix/src/posix.c
+++ b/xlators/storage/posix/src/posix.c
@@ -821,6 +821,7 @@ posix_do_zerofill (call_frame_t *frame, xlator_t *this, fd_t *fd, off_t offset,
 {
         int32_t            ret       = -1;
         int32_t            op_errno  = 0;
+        int32_t            flags     = 0;
         struct posix_fd   *pfd       = NULL;
         gf_boolean_t       locked    = _gf_false;
 
@@ -851,6 +852,14 @@ posix_do_zerofill (call_frame_t *frame, xlator_t *this, fd_t *fd, off_t offset,
                 goto out;
         }
 
+        /* See if we can use FALLOC_FL_ZERO_RANGE to perform the zero fill.
+         * If it fails, fall back to _posix_do_zerofill() and an optional fsync.
+         */
+        flags = FALLOC_FL_ZERO_RANGE;
+        ret = sys_fallocate (pfd->fd, flags, offset, len);
+        if (ret == 0)
+                goto done;
+
         ret = _posix_do_zerofill (pfd->fd, offset, len, pfd->flags & O_DIRECT);
         if (ret < 0) {
                 ret = -errno;
@@ -871,6 +880,7 @@ posix_do_zerofill (call_frame_t *frame, xlator_t *this, fd_t *fd, off_t offset,
                 }
         }
 
+done:
         ret = posix_fdstat (this, pfd->fd, statpost);
         if (ret == -1) {
                 ret = -errno;