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>

2 files changed, 37 insertions, 0 deletions

diff --git a/fs/xfs/linux-2.6/xfs_buf.c b/fs/xfs/linux-2.6/xfs_buf.c
index eca945b0f88f..22c7bff77ad2 100644
--- 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 fb30447091d8..57eedc750ee6 100644
--- 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 *);