cleanup blockdev_direct_IO locking

Currently the locking in blockdev_direct_IO is a mess, we have three different
locking types and very confusing checks for some of them.  The most
complicated one is DIO_OWN_LOCKING for reads, which happens to not actually be
used.

This patch gets rid of the DIO_OWN_LOCKING - as mentioned above the read case
is unused anyway, and the write side is almost identical to DIO_NO_LOCKING.
The difference is that DIO_NO_LOCKING always sets the create argument for
the get_blocks callback to zero, but we can easily move that to the actual
get_blocks callbacks.  There are four users of the DIO_NO_LOCKING mode:
gfs already ignores the create argument and thus is fine with the new
version, ocfs2 only errors out if create were ever set, and we can remove
this dead code now, the block device code only ever uses create for an
error message if we are fully beyond the device which can never happen,
and last but not least XFS will need the new behavour for writes.

Now we can replace the lock_type variable with a flags one, where no flag
means the DIO_NO_LOCKING behaviour and DIO_LOCKING is kept as the first
flag.  Separate out the check for not allowing to fill holes into a separate
flag, although for now both flags always get set at the same time.

Also revamp the documentation of the locking scheme to actually make sense.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 4 insertions, 30 deletions

diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
index deb2b132ae5e..3dae4a13f6e4 100644
--- a/fs/ocfs2/aops.c
+++ b/fs/ocfs2/aops.c
@@ -547,6 +547,9 @@ bail:
  *
  * called like this: dio->get_blocks(dio->inode, fs_startblk,
  *                                      fs_count, map_bh, dio->rw == WRITE);
+ *
+ * Note that we never bother to allocate blocks here, and thus ignore the
+ * create argument.
  */
 static int ocfs2_direct_IO_get_blocks(struct inode *inode, sector_t iblock,
                                      struct buffer_head *bh_result, int create)
@@ -563,14 +566,6 @@ static int ocfs2_direct_IO_get_blocks(struct inode *inode, sector_t iblock,
 
         inode_blocks = ocfs2_blocks_for_bytes(inode->i_sb, i_size_read(inode));
 
-        /*
-         * Any write past EOF is not allowed because we'd be extending.
-         */
-        if (create && (iblock + max_blocks) > inode_blocks) {
-                ret = -EIO;
-                goto bail;
-        }
-
         /* This figures out the size of the next contiguous block, and
          * our logical offset */
         ret = ocfs2_extent_map_get_blocks(inode, iblock, &p_blkno,
@@ -582,15 +577,6 @@ static int ocfs2_direct_IO_get_blocks(struct inode *inode, sector_t iblock,
                 goto bail;
         }
 
-        if (!ocfs2_sparse_alloc(OCFS2_SB(inode->i_sb)) && !p_blkno && create) {
-                ocfs2_error(inode->i_sb,
-                            "Inode %llu has a hole at block %llu\n",
-                            (unsigned long long)OCFS2_I(inode)->ip_blkno,
-                            (unsigned long long)iblock);
-                ret = -EROFS;
-                goto bail;
-        }
-
         /* We should already CoW the refcounted extent. */
         BUG_ON(ext_flags & OCFS2_EXT_REFCOUNTED);
         /*
@@ -601,20 +587,8 @@ static int ocfs2_direct_IO_get_blocks(struct inode *inode, sector_t iblock,
          */
         if (p_blkno && !(ext_flags & OCFS2_EXT_UNWRITTEN))
                 map_bh(bh_result, inode->i_sb, p_blkno);
-        else {
-                /*
-                 * ocfs2_prepare_inode_for_write() should have caught
-                 * the case where we'd be filling a hole and triggered
-                 * a buffered write instead.
-                 */
-                if (create) {
-                        ret = -EIO;
-                        mlog_errno(ret);
-                        goto bail;
-                }
-
+        else
                 clear_buffer_mapped(bh_result);
-        }
 
         /* make sure we don't map more than max_blocks blocks here as
            that's all the kernel will handle at this point. */