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From 4a1e019ac51460ce6329892cc99fc11d518d2eb2 Mon Sep 17 00:00:00 2001
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Message-Id: <4a1e019ac51460ce6329892cc99fc11d518d2eb2.1389014116.git.minovotn@redhat.com>
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In-Reply-To: <c8cc35838d42aa286242772d97e3a9be7bb786ba.1389014116.git.minovotn@redhat.com>
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References: <c8cc35838d42aa286242772d97e3a9be7bb786ba.1389014116.git.minovotn@redhat.com>
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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Mon, 9 Dec 2013 14:09:16 +0100
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Subject: [PATCH 28/50] block: make bdrv_co_do_write_zeroes stricter in
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 producing aligned requests
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RH-Author: Paolo Bonzini <pbonzini@redhat.com>
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Message-id: <1386598178-11845-31-git-send-email-pbonzini@redhat.com>
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Patchwork-id: 56067
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O-Subject: [RHEL 7.0 qemu-kvm PATCH 30/52] block: make bdrv_co_do_write_zeroes stricter in producing aligned requests
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Bugzilla: 1007815
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RH-Acked-by: Jeffrey Cody <jcody@redhat.com>
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RH-Acked-by: Fam Zheng <famz@redhat.com>
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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Right now, bdrv_co_do_write_zeroes will only try to align the
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beginning of the request.  However, it is simpler for many
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formats to expect the block layer to separate both the head *and*
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the tail.  This makes sure that the format's bdrv_co_write_zeroes
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function will be called with aligned sector_num and nb_sectors for
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the bulk of the request.
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Reviewed-by: Peter Lieven <pl@kamp.de>
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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(cherry picked from commit b8d71c09f31a9cae248d167dddc75c66d5135ff2)
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---
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 block.c | 35 +++++++++++++++++++++++------------
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 1 file changed, 23 insertions(+), 12 deletions(-)
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Signed-off-by: Michal Novotny <minovotn@redhat.com>
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---
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 block.c | 35 +++++++++++++++++++++++------------
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 1 file changed, 23 insertions(+), 12 deletions(-)
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diff --git a/block.c b/block.c
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index c9e65b4..1ac1ab3 100644
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--- a/block.c
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+++ b/block.c
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@@ -2781,14 +2781,21 @@ static int coroutine_fn bdrv_co_do_write_zeroes(BlockDriverState *bs,
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     while (nb_sectors > 0 && !ret) {
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         int num = nb_sectors;
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-        /* align request */
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-        if (bs->bl.write_zeroes_alignment &&
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-            num >= bs->bl.write_zeroes_alignment &&
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-            sector_num % bs->bl.write_zeroes_alignment) {
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-            if (num > bs->bl.write_zeroes_alignment) {
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+        /* Align request.  Block drivers can expect the "bulk" of the request
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+         * to be aligned.
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+         */
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+        if (bs->bl.write_zeroes_alignment
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+            && num > bs->bl.write_zeroes_alignment) {
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+            if (sector_num % bs->bl.write_zeroes_alignment != 0) {
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+                /* Make a small request up to the first aligned sector.  */
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                 num = bs->bl.write_zeroes_alignment;
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+                num -= sector_num % bs->bl.write_zeroes_alignment;
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+            } else if ((sector_num + num) % bs->bl.write_zeroes_alignment != 0) {
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+                /* Shorten the request to the last aligned sector.  num cannot
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+                 * underflow because num > bs->bl.write_zeroes_alignment.
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+                 */
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+                num -= (sector_num + num) % bs->bl.write_zeroes_alignment;
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             }
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-            num -= sector_num % bs->bl.write_zeroes_alignment;
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         }
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         /* limit request size */
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@@ -2806,16 +2813,20 @@ static int coroutine_fn bdrv_co_do_write_zeroes(BlockDriverState *bs,
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             /* Fall back to bounce buffer if write zeroes is unsupported */
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             iov.iov_len = num * BDRV_SECTOR_SIZE;
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             if (iov.iov_base == NULL) {
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-                /* allocate bounce buffer only once and ensure that it
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-                 * is big enough for this and all future requests.
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-                 */
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-                size_t bufsize = num <= nb_sectors ? num : max_write_zeroes;
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-                iov.iov_base = qemu_blockalign(bs, bufsize * BDRV_SECTOR_SIZE);
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-                memset(iov.iov_base, 0, bufsize * BDRV_SECTOR_SIZE);
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+                iov.iov_base = qemu_blockalign(bs, num * BDRV_SECTOR_SIZE);
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+                memset(iov.iov_base, 0, num * BDRV_SECTOR_SIZE);
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             }
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             qemu_iovec_init_external(&qiov, &iov, 1);
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             ret = drv->bdrv_co_writev(bs, sector_num, num, &qiov);
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+
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+            /* Keep bounce buffer around if it is big enough for all
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+             * all future requests.
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+             */
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+            if (num < max_write_zeroes) {
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+                qemu_vfree(iov.iov_base);
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+                iov.iov_base = NULL;
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+            }
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         }
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         sector_num += num;
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-- 
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1.7.11.7
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