GFS2: high time to take some time over atime

Until now, we've used the same scheme as GFS1 for atime. This has failed
since atime is a per vfsmnt flag, not a per fs flag and as such the
"noatime" flag was not getting passed down to the filesystems. This
patch removes all the "special casing" around atime updates and we
simply use the VFS's atime code.

The net result is that GFS2 will now support all the same atime related
mount options of any other filesystem on a per-vfsmnt basis. We do lose
the "lazy atime" updates, but we gain "relatime". We could add lazy
atime to the VFS at a later date, if there is a requirement for that
variant still - I suspect relatime will be enough.

Also we lose about 100 lines of code after this patch has been applied,
and I have a suspicion that it will speed things up a bit, even when
atime is "on". So it seems like a nice clean up as well.

From a user perspective, everything stays the same except the loss of
the per-fs atime quantum tweekable (ought to be per-vfsmnt at the very
least, and to be honest I don't think anybody ever used it) and that a
number of options which were ignored before now work correctly.

Please let me know if you've got any comments. I'm pushing this out
early so that you can all see what my plans are.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 8 insertions, 99 deletions

diff --git a/fs/gfs2/inode.c b/fs/gfs2/inode.c
index c8a959c09f1..7cee695fa44 100644
--- a/fs/gfs2/inode.c
+++ b/fs/gfs2/inode.c
@@ -18,6 +18,7 @@
 #include <linux/crc32.h>
 #include <linux/lm_interface.h>
 #include <linux/security.h>
+#include <linux/time.h>
 
 #include "gfs2.h"
 #include "incore.h"
@@ -249,6 +250,7 @@ static int gfs2_dinode_in(struct gfs2_inode *ip, const void *buf)
 {
 	struct gfs2_dinode_host *di = &ip->i_di;
 	const struct gfs2_dinode *str = buf;
+	struct timespec atime;
 	u16 height, depth;
 
 	if (unlikely(ip->i_no_addr != be64_to_cpu(str->di_num.no_addr)))
@@ -275,8 +277,10 @@ static int gfs2_dinode_in(struct gfs2_inode *ip, const void *buf)
 	di->di_size = be64_to_cpu(str->di_size);
 	i_size_write(&ip->i_inode, di->di_size);
 	gfs2_set_inode_blocks(&ip->i_inode, be64_to_cpu(str->di_blocks));
-	ip->i_inode.i_atime.tv_sec = be64_to_cpu(str->di_atime);
-	ip->i_inode.i_atime.tv_nsec = be32_to_cpu(str->di_atime_nsec);
+	atime.tv_sec = be64_to_cpu(str->di_atime);
+	atime.tv_nsec = be32_to_cpu(str->di_atime_nsec);
+	if (timespec_compare(&ip->i_inode.i_atime, &atime) < 0)
+		ip->i_inode.i_atime = atime;
 	ip->i_inode.i_mtime.tv_sec = be64_to_cpu(str->di_mtime);
 	ip->i_inode.i_mtime.tv_nsec = be32_to_cpu(str->di_mtime_nsec);
 	ip->i_inode.i_ctime.tv_sec = be64_to_cpu(str->di_ctime);
@@ -1157,8 +1161,8 @@ int gfs2_readlinki(struct gfs2_inode *ip, char **buf, unsigned int *len)
 	unsigned int x;
 	int error;
 
-	gfs2_holder_init(ip->i_gl, LM_ST_SHARED, GL_ATIME, &i_gh);
-	error = gfs2_glock_nq_atime(&i_gh);
+	gfs2_holder_init(ip->i_gl, LM_ST_SHARED, 0, &i_gh);
+	error = gfs2_glock_nq(&i_gh);
 	if (error) {
 		gfs2_holder_uninit(&i_gh);
 		return error;
@@ -1193,101 +1197,6 @@ out:
 	return error;
 }
 
-/**
- * gfs2_glock_nq_atime - Acquire a hold on an inode's glock, and
- *       conditionally update the inode's atime
- * @gh: the holder to acquire
- *
- * Tests atime (access time) for gfs2_read, gfs2_readdir and gfs2_mmap
- * Update if the difference between the current time and the inode's current
- * atime is greater than an interval specified at mount.
- *
- * Returns: errno
- */
-
-int gfs2_glock_nq_atime(struct gfs2_holder *gh)
-{
-	struct gfs2_glock *gl = gh->gh_gl;
-	struct gfs2_sbd *sdp = gl->gl_sbd;
-	struct gfs2_inode *ip = gl->gl_object;
-	s64 quantum = gfs2_tune_get(sdp, gt_atime_quantum);
-	unsigned int state;
-	int flags;
-	int error;
-	struct timespec tv = CURRENT_TIME;
-
-	if (gfs2_assert_warn(sdp, gh->gh_flags & GL_ATIME) ||
-	    gfs2_assert_warn(sdp, !(gh->gh_flags & GL_ASYNC)) ||
-	    gfs2_assert_warn(sdp, gl->gl_ops == &gfs2_inode_glops))
-		return -EINVAL;
-
-	state = gh->gh_state;
-	flags = gh->gh_flags;
-
-	error = gfs2_glock_nq(gh);
-	if (error)
-		return error;
-
-	if (test_bit(SDF_NOATIME, &sdp->sd_flags) ||
-	    (sdp->sd_vfs->s_flags & MS_RDONLY))
-		return 0;
-
-	if (tv.tv_sec - ip->i_inode.i_atime.tv_sec >= quantum) {
-		gfs2_glock_dq(gh);
-		gfs2_holder_reinit(LM_ST_EXCLUSIVE, gh->gh_flags & ~LM_FLAG_ANY,
-				   gh);
-		error = gfs2_glock_nq(gh);
-		if (error)
-			return error;
-
-		/* Verify that atime hasn't been updated while we were
-		   trying to get exclusive lock. */
-
-		tv = CURRENT_TIME;
-		if (tv.tv_sec - ip->i_inode.i_atime.tv_sec >= quantum) {
-			struct buffer_head *dibh;
-			struct gfs2_dinode *di;
-
-			error = gfs2_trans_begin(sdp, RES_DINODE, 0);
-			if (error == -EROFS)
-				return 0;
-			if (error)
-				goto fail;
-
-			error = gfs2_meta_inode_buffer(ip, &dibh);
-			if (error)
-				goto fail_end_trans;
-
-			ip->i_inode.i_atime = tv;
-
-			gfs2_trans_add_bh(ip->i_gl, dibh, 1);
-			di = (struct gfs2_dinode *)dibh->b_data;
-			di->di_atime = cpu_to_be64(ip->i_inode.i_atime.tv_sec);
-			di->di_atime_nsec = cpu_to_be32(ip->i_inode.i_atime.tv_nsec);
-			brelse(dibh);
-
-			gfs2_trans_end(sdp);
-		}
-
-		/* If someone else has asked for the glock,
-		   unlock and let them have it. Then reacquire
-		   in the original state. */
-		if (gfs2_glock_is_blocking(gl)) {
-			gfs2_glock_dq(gh);
-			gfs2_holder_reinit(state, flags, gh);
-			return gfs2_glock_nq(gh);
-		}
-	}
-
-	return 0;
-
-fail_end_trans:
-	gfs2_trans_end(sdp);
-fail:
-	gfs2_glock_dq(gh);
-	return error;
-}
-
 static int
 __gfs2_setattr_simple(struct gfs2_inode *ip, struct iattr *attr)
 {