xfs: introduced uncached buffer read primitve

To avoid the need to use cached buffers for single-shot or buffers
cached at the filesystem level, introduce a new buffer read
primitive that bypasses the cache an reads directly from disk.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>

diff --git a/fs/xfs/linux-2.6/xfs_buf.c b/fs/xfs/linux-2.6/xfs_buf.c
index eca945b0f88f3f394b58730bbb789823f74dd6af..22c7bff77ad2f1b4ef2182806ddde440ba78b9a7 100644 (file)
--- a/fs/xfs/linux-2.6/xfs_buf.c
+++ b/fs/xfs/linux-2.6/xfs_buf.c
@@ -638,6 +638,40 @@ xfs_buf_readahead(
        xfs_buf_read(target, ioff, isize, flags);
 }
 
+/*
+ * Read an uncached buffer from disk. Allocates and returns a locked
+ * buffer containing the disk contents or nothing.
+ */
+struct xfs_buf *
+xfs_buf_read_uncached(
+       struct xfs_mount        *mp,
+       struct xfs_buftarg      *target,
+       xfs_daddr_t             daddr,
+       size_t                  length,
+       int                     flags)
+{
+       xfs_buf_t               *bp;
+       int                     error;
+
+       bp = xfs_buf_get_uncached(target, length, flags);
+       if (!bp)
+               return NULL;
+
+       /* set up the buffer for a read IO */
+       xfs_buf_lock(bp);
+       XFS_BUF_SET_ADDR(bp, daddr);
+       XFS_BUF_READ(bp);
+       XFS_BUF_BUSY(bp);
+
+       xfsbdstrat(mp, bp);
+       error = xfs_iowait(bp);
+       if (error || bp->b_error) {
+               xfs_buf_relse(bp);
+               return NULL;
+       }
+       return bp;
+}
+
 xfs_buf_t *
 xfs_buf_get_empty(
        size_t                  len,

diff --git a/fs/xfs/linux-2.6/xfs_buf.h b/fs/xfs/linux-2.6/xfs_buf.h
index fb30447091d83e1cab41e41580491b066c0dbba9..57eedc750ee6727168604f558b705da151a63b9e 100644 (file)
--- a/fs/xfs/linux-2.6/xfs_buf.h
+++ b/fs/xfs/linux-2.6/xfs_buf.h
@@ -218,6 +218,9 @@ extern int xfs_buf_associate_memory(xfs_buf_t *, void *, size_t);
 extern void xfs_buf_hold(xfs_buf_t *);
 extern void xfs_buf_readahead(xfs_buftarg_t *, xfs_off_t, size_t,
                                xfs_buf_flags_t);
+struct xfs_buf *xfs_buf_read_uncached(struct xfs_mount *mp,
+                               struct xfs_buftarg *target,
+                               xfs_daddr_t daddr, size_t length, int flags);
 
 /* Releasing Buffers */
 extern void xfs_buf_free(xfs_buf_t *);