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[PATCH 3/9] xfs: convert internal buffer functions to pass maps

To: xfs@xxxxxxxxxxx
Subject: [PATCH 3/9] xfs: convert internal buffer functions to pass maps
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Fri, 22 Jun 2012 18:50:09 +1000
In-reply-to: <1340355015-26250-1-git-send-email-david@xxxxxxxxxxxxx>
References: <1340355015-26250-1-git-send-email-david@xxxxxxxxxxxxx>
From: Dave Chinner <dchinner@xxxxxxxxxx>

While the external interface currently uses separate blockno/length
variables, we need to move internal interfaces to passing and
parsing vector maps. This will then allow us to add external
interfaces to support discontiguous buffer maps as the internal code
will already support them.

Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
---
 fs/xfs/xfs_buf.c |  202 +++++++++++++++++++++++++++++++++++++++++-------------
 fs/xfs/xfs_buf.h |   43 +++++++++---
 2 files changed, 191 insertions(+), 54 deletions(-)

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index a843873..82bb812 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -164,14 +164,49 @@ xfs_buf_stale(
        ASSERT(atomic_read(&bp->b_hold) >= 1);
 }
 
+static int
+xfs_buf_get_maps(
+       struct xfs_buf          *bp,
+       int                     map_count)
+{
+       ASSERT(bp->b_maps == NULL);
+       bp->b_map_count = map_count;
+
+       if (map_count == 1) {
+               bp->b_maps = &bp->b_map;
+               return 0;
+       }
+
+       bp->b_maps = kmem_zalloc(map_count * sizeof(struct xfs_buf_map),
+                               KM_NOFS);
+       if (!bp->b_maps)
+               return ENOMEM;
+       return 0;
+}
+
+/*
+ *     Frees b_pages if it was allocated.
+ */
+static void
+xfs_buf_free_maps(
+       struct xfs_buf  *bp)
+{
+       if (bp->b_maps != &bp->b_map) {
+               kmem_free(bp->b_maps);
+               bp->b_maps = NULL;
+       }
+}
+
 struct xfs_buf *
-xfs_buf_alloc(
+_xfs_buf_alloc(
        struct xfs_buftarg      *target,
-       xfs_daddr_t             blkno,
-       size_t                  numblks,
+       struct xfs_buf_map      *map,
+       int                     nmaps,
        xfs_buf_flags_t         flags)
 {
        struct xfs_buf          *bp;
+       int                     error;
+       int                     i;
 
        bp = kmem_zone_zalloc(xfs_buf_zone, KM_NOFS);
        if (unlikely(!bp))
@@ -192,18 +227,28 @@ xfs_buf_alloc(
        sema_init(&bp->b_sema, 0); /* held, no waiters */
        XB_SET_OWNER(bp);
        bp->b_target = target;
+       bp->b_flags = flags;
 
        /*
         * Set length and io_length to the same value initially.
         * I/O routines should use io_length, which will be the same in
         * most cases but may be reset (e.g. XFS recovery).
         */
-       bp->b_length = numblks;
-       bp->b_io_length = numblks;
-       bp->b_flags = flags;
-       bp->b_bn = blkno;
-       bp->b_map.bm_bn = blkno;
-       bp->b_map.bm_len = numblks;
+       error = xfs_buf_get_maps(bp, nmaps);
+       if (error)  {
+               kmem_zone_free(xfs_buf_zone, bp);
+               return NULL;
+       }
+
+       bp->b_bn = map[0].bm_bn;
+       bp->b_length = 0;
+       for (i = 0; i < nmaps; i++) {
+               bp->b_maps[i].bm_bn = map[i].bm_bn;
+               bp->b_maps[i].bm_len = map[i].bm_len;
+               bp->b_length += map[i].bm_len;
+       }
+       bp->b_io_length = bp->b_length;
+
        atomic_set(&bp->b_pin_count, 0);
        init_waitqueue_head(&bp->b_waiters);
 
@@ -282,6 +327,7 @@ xfs_buf_free(
        } else if (bp->b_flags & _XBF_KMEM)
                kmem_free(bp->b_addr);
        _xfs_buf_free_pages(bp);
+       xfs_buf_free_maps(bp);
        kmem_zone_free(xfs_buf_zone, bp);
 }
 
@@ -428,8 +474,8 @@ _xfs_buf_map_pages(
 xfs_buf_t *
 _xfs_buf_find(
        struct xfs_buftarg      *btp,
-       xfs_daddr_t             blkno,
-       size_t                  numblks,
+       struct xfs_buf_map      *map,
+       int                     nmaps,
        xfs_buf_flags_t         flags,
        xfs_buf_t               *new_bp)
 {
@@ -438,7 +484,12 @@ _xfs_buf_find(
        struct rb_node          **rbp;
        struct rb_node          *parent;
        xfs_buf_t               *bp;
+       xfs_daddr_t             blkno = map[0].bm_bn;
+       int                     numblks = 0;
+       int                     i;
 
+       for (i = 0; i < nmaps; i++)
+               numblks += map[i].bm_len;
        numbytes = BBTOB(numblks);
 
        /* Check for IOs smaller than the sector size / not sector aligned */
@@ -539,22 +590,23 @@ xfs_buf_get(
        struct xfs_buf          *bp;
        struct xfs_buf          *new_bp;
        int                     error = 0;
+       DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
 
-       bp = _xfs_buf_find(target, blkno, numblks, flags, NULL);
+       bp = _xfs_buf_find(target, &map, 1, flags, NULL);
        if (likely(bp))
                goto found;
 
-       new_bp = xfs_buf_alloc(target, blkno, numblks, flags);
+       new_bp = _xfs_buf_alloc(target, &map, 1, flags);
        if (unlikely(!new_bp))
                return NULL;
 
        error = xfs_buf_allocate_memory(new_bp, flags);
        if (error) {
-               kmem_zone_free(xfs_buf_zone, new_bp);
+               xfs_buf_free(new_bp);
                return NULL;
        }
 
-       bp = _xfs_buf_find(target, blkno, numblks, flags, new_bp);
+       bp = _xfs_buf_find(target, &map, 1, flags, new_bp);
        if (!bp) {
                xfs_buf_free(new_bp);
                return NULL;
@@ -666,7 +718,9 @@ xfs_buf_read_uncached(
                return NULL;
 
        /* set up the buffer for a read IO */
-       bp->b_map.bm_bn = daddr;
+       ASSERT(bp->b_map_count == 1);
+       bp->b_bn = daddr;
+       bp->b_maps[0].bm_bn = daddr;
        bp->b_flags |= XBF_READ;
 
        xfsbdstrat(target->bt_mount, bp);
@@ -695,9 +749,11 @@ xfs_buf_set_empty(
        bp->b_addr = NULL;
        bp->b_length = numblks;
        bp->b_io_length = numblks;
+
+       ASSERT(bp->b_map_count == 1);
        bp->b_bn = XFS_BUF_DADDR_NULL;
-       bp->b_map.bm_bn = XFS_BUF_DADDR_NULL;
-       bp->b_map.bm_len = bp->b_length;
+       bp->b_maps[0].bm_bn = XFS_BUF_DADDR_NULL;
+       bp->b_maps[0].bm_len = bp->b_length;
 }
 
 static inline struct page *
@@ -761,9 +817,10 @@ xfs_buf_get_uncached(
 {
        unsigned long           page_count;
        int                     error, i;
-       xfs_buf_t               *bp;
+       struct xfs_buf          *bp;
+       DEFINE_SINGLE_BUF_MAP(map, XFS_BUF_DADDR_NULL, numblks);
 
-       bp = xfs_buf_alloc(target, XFS_BUF_DADDR_NULL, numblks, 0);
+       bp = _xfs_buf_alloc(target, &map, 1, 0);
        if (unlikely(bp == NULL))
                goto fail;
 
@@ -794,6 +851,7 @@ xfs_buf_get_uncached(
                __free_page(bp->b_pages[i]);
        _xfs_buf_free_pages(bp);
  fail_free_buf:
+       xfs_buf_free_maps(bp);
        kmem_zone_free(xfs_buf_zone, bp);
  fail:
        return NULL;
@@ -1154,36 +1212,39 @@ xfs_buf_bio_end_io(
        bio_put(bio);
 }
 
-STATIC void
-_xfs_buf_ioapply(
-       xfs_buf_t               *bp)
+static void
+xfs_buf_ioapply_map(
+       struct xfs_buf  *bp,
+       int             map,
+       int             *buf_offset,
+       int             *count,
+       int             rw)
 {
-       int                     rw, map_i, total_nr_pages, nr_pages;
-       struct bio              *bio;
-       int                     offset = bp->b_offset;
-       int                     size = BBTOB(bp->b_io_length);
-       sector_t                sector = bp->b_map.bm_bn;
+       int             page_index;
+       int             total_nr_pages = bp->b_page_count;
+       int             nr_pages;
+       struct bio      *bio;
+       sector_t        sector =  bp->b_maps[map].bm_bn;
+       int             size;
+       int             offset;
 
        total_nr_pages = bp->b_page_count;
-       map_i = 0;
 
-       if (bp->b_flags & XBF_WRITE) {
-               if (bp->b_flags & XBF_SYNCIO)
-                       rw = WRITE_SYNC;
-               else
-                       rw = WRITE;
-               if (bp->b_flags & XBF_FUA)
-                       rw |= REQ_FUA;
-               if (bp->b_flags & XBF_FLUSH)
-                       rw |= REQ_FLUSH;
-       } else if (bp->b_flags & XBF_READ_AHEAD) {
-               rw = READA;
-       } else {
-               rw = READ;
+       /* skip the pages in the buffer before the start offset */
+       page_index = 0;
+       offset = *buf_offset;
+       while (offset >= PAGE_SIZE) {
+               page_index++;
+               offset -= PAGE_SIZE;
        }
 
-       /* we only use the buffer cache for meta-data */
-       rw |= REQ_META;
+       /*
+        * Limit the IO size to the length of the current vector, and update the
+        * remaining IO count for the next time around.
+        */
+       size = min_t(int, BBTOB(bp->b_maps[map].bm_len), *count);
+       *count -= size;
+       *buf_offset += size;
 
 next_chunk:
        atomic_inc(&bp->b_io_remaining);
@@ -1198,13 +1259,14 @@ next_chunk:
        bio->bi_private = bp;
 
 
-       for (; size && nr_pages; nr_pages--, map_i++) {
+       for (; size && nr_pages; nr_pages--, page_index++) {
                int     rbytes, nbytes = PAGE_SIZE - offset;
 
                if (nbytes > size)
                        nbytes = size;
 
-               rbytes = bio_add_page(bio, bp->b_pages[map_i], nbytes, offset);
+               rbytes = bio_add_page(bio, bp->b_pages[page_index], nbytes,
+                                     offset);
                if (rbytes < nbytes)
                        break;
 
@@ -1226,6 +1288,54 @@ next_chunk:
                xfs_buf_ioerror(bp, EIO);
                bio_put(bio);
        }
+
+}
+
+STATIC void
+_xfs_buf_ioapply(
+       struct xfs_buf  *bp)
+{
+       struct blk_plug plug;
+       int             rw;
+       int             offset;
+       int             size;
+       int             i;
+
+       if (bp->b_flags & XBF_WRITE) {
+               if (bp->b_flags & XBF_SYNCIO)
+                       rw = WRITE_SYNC;
+               else
+                       rw = WRITE;
+               if (bp->b_flags & XBF_FUA)
+                       rw |= REQ_FUA;
+               if (bp->b_flags & XBF_FLUSH)
+                       rw |= REQ_FLUSH;
+       } else if (bp->b_flags & XBF_READ_AHEAD) {
+               rw = READA;
+       } else {
+               rw = READ;
+       }
+
+       /* we only use the buffer cache for meta-data */
+       rw |= REQ_META;
+
+       /*
+        * Walk all the vectors issuing IO on them. Set up the initial offset
+        * into the buffer and the desired IO size before we start -
+        * _xfs_buf_ioapply_vec() will modify them appropriately for each
+        * subsequent call.
+        */
+       offset = bp->b_offset;
+       size = BBTOB(bp->b_io_length);
+       blk_start_plug(&plug);
+       for (i = 0; i < bp->b_map_count; i++) {
+               xfs_buf_ioapply_map(bp, i, &offset, &size, rw);
+               if (bp->b_error)
+                       break;
+               if (size <= 0)
+                       break;  /* all done */
+       }
+       blk_finish_plug(&plug);
 }
 
 void
diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index c9c2ba9..67d1349 100644
--- a/fs/xfs/xfs_buf.h
+++ b/fs/xfs/xfs_buf.h
@@ -105,6 +105,9 @@ struct xfs_buf_map {
        int                     bm_len; /* size of I/O */
 };
 
+#define DEFINE_SINGLE_BUF_MAP(map, blkno, numblk) \
+       struct xfs_buf_map (map) = { .bm_bn = (blkno), .bm_len = (numblk) };
+
 typedef struct xfs_buf {
        /*
         * first cacheline holds all the fields needed for an uncontended cache
@@ -134,7 +137,9 @@ typedef struct xfs_buf {
        struct xfs_trans        *b_transp;
        struct page             **b_pages;      /* array of page pointers */
        struct page             *b_page_array[XB_PAGES]; /* inline pages */
-       struct xfs_buf_map      b_map;          /* compound buffer map */
+       struct xfs_buf_map      *b_maps;        /* compound buffer map */
+       struct xfs_buf_map      b_map;          /* inline compound buffer map */
+       int                     b_map_count;
        int                     b_io_length;    /* IO size in BBs */
        atomic_t                b_pin_count;    /* pin count */
        atomic_t                b_io_remaining; /* #outstanding I/O requests */
@@ -149,11 +154,35 @@ typedef struct xfs_buf {
 
 
 /* Finding and Reading Buffers */
-struct xfs_buf *_xfs_buf_find(struct xfs_buftarg *target, xfs_daddr_t blkno,
-                               size_t numblks, xfs_buf_flags_t flags,
-                               struct xfs_buf *new_bp);
-#define xfs_incore(buftarg,blkno,len,lockit) \
-       _xfs_buf_find(buftarg, blkno ,len, lockit, NULL)
+struct xfs_buf *_xfs_buf_find(struct xfs_buftarg *target,
+                             struct xfs_buf_map *map, int nmaps,
+                             xfs_buf_flags_t flags, struct xfs_buf *new_bp);
+
+static inline struct xfs_buf *
+xfs_incore(
+       struct xfs_buftarg      *target,
+       xfs_daddr_t             blkno,
+       size_t                  numblks,
+       xfs_buf_flags_t         flags)
+{
+       DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
+       return _xfs_buf_find(target, &map, 1, flags, NULL);
+}
+
+struct xfs_buf *_xfs_buf_alloc(struct xfs_buftarg *target,
+                              struct xfs_buf_map *map, int nmaps,
+                              xfs_buf_flags_t flags);
+
+static inline struct xfs_buf *
+xfs_buf_alloc(
+       struct xfs_buftarg      *target,
+       xfs_daddr_t             blkno,
+       size_t                  numblks,
+       xfs_buf_flags_t         flags)
+{
+       DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
+       return _xfs_buf_alloc(target, &map, 1, flags);
+}
 
 struct xfs_buf *xfs_buf_get(struct xfs_buftarg *target, xfs_daddr_t blkno,
                                size_t numblks, xfs_buf_flags_t flags);
@@ -163,8 +192,6 @@ void xfs_buf_readahead(struct xfs_buftarg *target, 
xfs_daddr_t blkno,
                                size_t numblks);
 
 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);
 void xfs_buf_set_empty(struct xfs_buf *bp, size_t numblks);
 int xfs_buf_associate_memory(struct xfs_buf *bp, void *mem, size_t length);
 
-- 
1.7.10

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