[PATCH 06/16] xfs: introduced uncached buffer read primitve

Dave Chinner
2010-09-22T06:43:57Z

From: Dave Chinner <dchinner@redhat.com>

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>
---
fs/xfs/linux-2.6/xfs_buf.c | 34 ++++++++++++++++++++++++++++++++++
fs/xfs/linux-2.6/xfs_buf.h | 3 +++
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 fbbc6d3..c8420c0 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(length, flags, target);
+ 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 fbcc77b..23da2aa 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 *);
--
1.7.1