Blame SOURCES/kvm-block-honour-BlockLimits-in-bdrv_co_do_write_zeroes.patch.patch.patch

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From 69e802baf506bd21a2f444cfebe4ac7f5b5d07a8 Mon Sep 17 00:00:00 2001
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Message-Id: <69e802baf506bd21a2f444cfebe4ac7f5b5d07a8.1389014116.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 14:09:02 +0100
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Subject: [PATCH 14/50] block: honour BlockLimits in bdrv_co_do_write_zeroes
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RH-Author: Paolo Bonzini <pbonzini@redhat.com>
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Message-id: <1386598178-11845-17-git-send-email-pbonzini@redhat.com>
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Patchwork-id: 56052
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O-Subject: [RHEL 7.0 qemu-kvm PATCH 16/52] block: honour BlockLimits in bdrv_co_do_write_zeroes
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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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From: Peter Lieven <pl@kamp.de>
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Reviewed-by: Eric Blake <eblake@redhat.com>
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Signed-off-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 c31cb70728d2c0c8900b35a66784baa446fd5147)
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---
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 block.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++++----------------
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 1 file changed, 49 insertions(+), 16 deletions(-)
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Signed-off-by: Michal Novotny <minovotn@redhat.com>
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---
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 block.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++++----------------
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 1 file changed, 49 insertions(+), 16 deletions(-)
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diff --git a/block.c b/block.c
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index 2fae459..2ed9aa9 100644
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--- a/block.c
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+++ b/block.c
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@@ -2724,32 +2724,65 @@ int coroutine_fn bdrv_co_copy_on_readv(BlockDriverState *bs,
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                             BDRV_REQ_COPY_ON_READ);
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 }
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+/* if no limit is specified in the BlockLimits use a default
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+ * of 32768 512-byte sectors (16 MiB) per request.
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+ */
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+#define MAX_WRITE_ZEROES_DEFAULT 32768
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+
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 static int coroutine_fn bdrv_co_do_write_zeroes(BlockDriverState *bs,
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     int64_t sector_num, int nb_sectors, BdrvRequestFlags flags)
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 {
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     BlockDriver *drv = bs->drv;
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     QEMUIOVector qiov;
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-    struct iovec iov;
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-    int ret;
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+    struct iovec iov = {0};
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+    int ret = 0;
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-    /* TODO Emulate only part of misaligned requests instead of letting block
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-     * drivers return -ENOTSUP and emulate everything */
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+    int max_write_zeroes = bs->bl.max_write_zeroes ?
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+                           bs->bl.max_write_zeroes : MAX_WRITE_ZEROES_DEFAULT;
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-    /* First try the efficient write zeroes operation */
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-    if (drv->bdrv_co_write_zeroes) {
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-        ret = drv->bdrv_co_write_zeroes(bs, sector_num, nb_sectors, flags);
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-        if (ret != -ENOTSUP) {
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-            return ret;
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+    while (nb_sectors > 0 && !ret) {
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+        int num = nb_sectors;
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+
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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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+                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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-    }
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-    /* Fall back to bounce buffer if write zeroes is unsupported */
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-    iov.iov_len  = nb_sectors * BDRV_SECTOR_SIZE;
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-    iov.iov_base = qemu_blockalign(bs, iov.iov_len);
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-    memset(iov.iov_base, 0, iov.iov_len);
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-    qemu_iovec_init_external(&qiov, &iov, 1);
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+        /* limit request size */
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+        if (num > max_write_zeroes) {
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+            num = max_write_zeroes;
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+        }
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+
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+        ret = -ENOTSUP;
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+        /* First try the efficient write zeroes operation */
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+        if (drv->bdrv_co_write_zeroes) {
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+            ret = drv->bdrv_co_write_zeroes(bs, sector_num, num, flags);
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+        }
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+
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+        if (ret == -ENOTSUP) {
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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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+            }
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+            qemu_iovec_init_external(&qiov, &iov, 1);
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-    ret = drv->bdrv_co_writev(bs, sector_num, nb_sectors, &qiov);
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+            ret = drv->bdrv_co_writev(bs, sector_num, num, &qiov);
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+        }
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+
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+        sector_num += num;
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+        nb_sectors -= num;
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+    }
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     qemu_vfree(iov.iov_base);
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     return ret;
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-- 
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1.7.11.7
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