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[PATCH 04/12] xfs: add compound buffer get and read interfaces

To: xfs@xxxxxxxxxxx
Subject: [PATCH 04/12] xfs: add compound buffer get and read interfaces
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Wed, 7 Dec 2011 17:18:15 +1100
In-reply-to: <1323238703-13198-1-git-send-email-david@xxxxxxxxxxxxx>
References: <1323238703-13198-1-git-send-email-david@xxxxxxxxxxxxx>
From: Dave Chinner <dchinner@xxxxxxxxxx>

For a compound buffer, we need to have some way of specifying all
the extents that need to be part of the buffer in one structure. The
dabuf code gets this directly from xfs_bmapi() in the form of an
xfs_bmbt_irec array. It makes sense to simply use this as the method
of transferring the information to the compound buffer get and read
functions that are responsible for building such buffers.

Implement the get and read compound buffer functions using this
interface. Initially only support a single irec map to simplify the
initial implementation. Support for multiple records will be added
in future commits.

Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
---
 fs/xfs/xfs_buf.c |   78 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 fs/xfs/xfs_buf.h |   10 +++++++
 2 files changed, 88 insertions(+), 0 deletions(-)

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 152e855..aebe954 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -40,6 +40,8 @@
 #include "xfs_ag.h"
 #include "xfs_mount.h"
 #include "xfs_trace.h"
+#include "xfs_bit.h"
+#include "xfs_bmap_btree.h"
 
 static kmem_zone_t *xfs_buf_zone;
 STATIC int xfsbufd(void *);
@@ -670,6 +672,82 @@ xfs_buf_readahead(
 }
 
 /*
+ * XXX: only supports a single map for now
+ */
+struct xfs_buf *
+xfs_buf_get_irec(
+       struct xfs_buftarg      *target,
+       struct xfs_bmbt_irec    *map,
+       int                     nmaps,
+       xfs_buf_flags_t         flags)
+{
+       xfs_daddr_t             blkno;
+       size_t                  numblks;
+       struct xfs_buf          *bp;
+
+       ASSERT_ALWAYS(nmaps == 1);
+
+       blkno = XFS_FSB_TO_DADDR(target->bt_mount, map->br_startblock);
+       numblks = XFS_FSB_TO_BB(target->bt_mount, map->br_blockcount);
+
+       bp = xfs_buf_get(target, blkno, numblks, flags);
+
+       return bp;
+}
+
+struct xfs_buf *
+xfs_buf_read_irec(
+       struct xfs_buftarg      *target,
+       struct xfs_bmbt_irec    *map,
+       int                     nmaps,
+       xfs_buf_flags_t         flags)
+{
+       xfs_buf_t               *bp;
+
+       flags |= XBF_READ;
+
+       bp = xfs_buf_get_irec(target, map, nmaps, flags);
+       if (bp) {
+               trace_xfs_buf_read(bp, flags, _RET_IP_);
+
+               if (!XFS_BUF_ISDONE(bp)) {
+                       XFS_STATS_INC(xb_get_read);
+                       _xfs_buf_read(bp, flags);
+               } else if (flags & XBF_ASYNC) {
+                       /*
+                        * Read ahead call which is already satisfied,
+                        * drop the buffer
+                        */
+                       goto no_buffer;
+               } else {
+                       /* We do not want read in the flags */
+                       bp->b_flags &= ~XBF_READ;
+               }
+       }
+
+       return bp;
+
+ no_buffer:
+       if (flags & (XBF_LOCK | XBF_TRYLOCK))
+               xfs_buf_unlock(bp);
+       xfs_buf_rele(bp);
+       return NULL;
+}
+
+void
+xfs_buf_readahead_irec(
+       struct xfs_buftarg      *target,
+       struct xfs_bmbt_irec    *map,
+       int                     nmaps)
+{
+       if (bdi_read_congested(target->bt_bdi))
+               return;
+
+       xfs_buf_read_irec(target, map, nmaps,
+                    XBF_TRYLOCK|XBF_ASYNC|XBF_READ_AHEAD|XBF_DONT_BLOCK);
+}
+
+/*
  * Read an uncached buffer from disk. Allocates and returns a locked
  * buffer containing the disk contents or nothing.
  */
diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index 1a3367e..e3cbd73 100644
--- a/fs/xfs/xfs_buf.h
+++ b/fs/xfs/xfs_buf.h
@@ -122,6 +122,7 @@ typedef void (*xfs_buf_iodone_t)(struct xfs_buf *);
 
 #define XB_PAGES       2
 
+struct xfs_bmbt_irec;
 struct xfs_buf_vec {
        xfs_daddr_t             bv_bn;  /* block number for I/O */
        size_t                  bv_len; /* size of I/O */
@@ -189,6 +190,15 @@ struct xfs_buf *xfs_buf_read(struct xfs_buftarg *target, 
xfs_daddr_t blkno,
 void xfs_buf_readahead(struct xfs_buftarg *target, xfs_daddr_t blkno,
                                size_t numblks);
 
+struct xfs_buf *xfs_buf_get_irec(struct xfs_buftarg *target,
+                               struct xfs_bmbt_irec *map, int nmaps,
+                               xfs_buf_flags_t flags);
+struct xfs_buf *xfs_buf_read_irec(struct xfs_buftarg *target,
+                               struct xfs_bmbt_irec *map, int nmaps,
+                               xfs_buf_flags_t flags);
+void xfs_buf_readahead_irec(struct xfs_buftarg *target,
+                               struct xfs_bmbt_irec *map, int nmaps);
+
 struct xfs_buf *xfs_buf_get_empty(struct xfs_buftarg *target, size_t numblks);
 struct xfs_buf *xfs_buf_alloc(struct xfs_buftarg *target, xfs_daddr_t blkno,
                                size_t numblks, xfs_buf_flags_t flags);
-- 
1.7.5.4

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