[GFS2] Put back O_DIRECT support

This patch adds back O_DIRECT support with various caveats
attached:

 1. Journaled data can be read via O_DIRECT since its now the
    same on disk format as normal data files.
 2. Journaled data writes with O_DIRECT will be failed sliently
    back to normal writes (should we really do this I wonder or
    should we return an error instead?)
 3. Stuffed files will be failed back to normal buffered I/O
 4. All the usual corner cases (write beyond current end of file,
    write to an unallocated block) will also revert to normal buffered I/O.

The I/O path is slightly odd as reads arrive at the page cache layer
with the lock for the file already held, but writes arrive unlocked.

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

1 files changed, 17 insertions, 12 deletions

diff --git a/fs/gfs2/ops_file.c b/fs/gfs2/ops_file.c
index 56820b39a993..bcde7a0b76f1 100644
--- a/fs/gfs2/ops_file.c
+++ b/fs/gfs2/ops_file.c
@@ -176,16 +176,16 @@ static ssize_t __gfs2_file_aio_read(struct kiocb *iocb,
                  * If any segment has a negative length, or the cumulative
                  * length ever wraps negative then return -EINVAL.
                  */
-        count += iv->iov_len;
-        if (unlikely((ssize_t)(count|iv->iov_len) < 0))
-                return -EINVAL;
-        if (access_ok(VERIFY_WRITE, iv->iov_base, iv->iov_len))
-                continue;
-        if (seg == 0)
-                return -EFAULT;
-        nr_segs = seg;
-        count -= iv->iov_len;   /* This segment is no good */
-        break;
+                count += iv->iov_len;
+                if (unlikely((ssize_t)(count|iv->iov_len) < 0))
+                        return -EINVAL;
+                if (access_ok(VERIFY_WRITE, iv->iov_base, iv->iov_len))
+                        continue;
+                if (seg == 0)
+                        return -EFAULT;
+                nr_segs = seg;
+                count -= iv->iov_len;   /* This segment is no good */
+                break;
         }
 
         /* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
@@ -204,10 +204,14 @@ static ssize_t __gfs2_file_aio_read(struct kiocb *iocb,
                 retval = gfs2_glock_nq_m_atime(1, &gh);
                 if (retval)
                         goto out;
-
+                if (gfs2_is_stuffed(ip)) {
+                        gfs2_glock_dq_m(1, &gh);
+                        gfs2_holder_uninit(&gh);
+                        goto fallback_to_normal;
+                }
                 size = i_size_read(inode);
                 if (pos < size) {
-                         retval = gfs2_direct_IO_read(iocb, iov, pos, nr_segs);
+                        retval = gfs2_direct_IO_read(iocb, iov, pos, nr_segs);
                         if (retval > 0 && !is_sync_kiocb(iocb))
                                 retval = -EIOCBQUEUED;
                         if (retval > 0)
@@ -219,6 +223,7 @@ static ssize_t __gfs2_file_aio_read(struct kiocb *iocb,
                 goto out;
         }
 
+fallback_to_normal:
         retval = 0;
         if (count) {
                 for (seg = 0; seg < nr_segs; seg++) {