[Qemu-devel] [PATCH v4 0/3] backup: Use copy offloading

[Qemu-devel] [PATCH v4 0/3] backup: Use copy offloading

[Fam Zheng]

v4: Rebase to master.
    Pick up Stefan's rev-bys.
    Include a block/io.c fix to fix a new issue caused by recent block/io.c
    change - our drive-backup cases in iotests exposes the bug loudly.

This enhances the backup job to make use of the copy offloading API. It
eliminates the necessity to use the bounce buffer as well as speeding up the
copy operation when the backend supports it.

v3: Don't forget coroutine_fn. [Stefan]
    Don't reset job->use_copy_range redundantly. [Stefan]

v2: Use helper functions. [Stefan]

Fam Zheng (3):
  block: Fix parameter checking in bdrv_co_copy_range_internal
  block: Honour BDRV_REQ_NO_SERIALISING in copy range
  backup: Use copy offloading

 block/backup.c        | 150 ++++++++++++++++++++++++++++++------------
 block/io.c            |  35 +++++-----
 block/trace-events    |   1 +
 include/block/block.h |   5 +-
 4 files changed, 132 insertions(+), 59 deletions(-)

-- 
2.17.1

[Qemu-devel] [PATCH v4 1/3] block: Fix parameter checking in bdrv_co_copy_range_internal

[Fam Zheng]

src may be NULL if BDRV_REQ_ZERO_WRITE flag is set, in this case only
check dst and dst->bs. This bug was introduced when moving in the
request tracking code from bdrv_co_copy_range, in 37aec7d75eb.

This especially fixes the possible segfault when initializing src_bs
with a NULL src.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block/io.c | 29 +++++++++++++++--------------
 1 file changed, 15 insertions(+), 14 deletions(-)

diff --git a/block/io.c b/block/io.c
index 7035b78a20..b8845708d7 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2897,18 +2897,11 @@ static int coroutine_fn bdrv_co_copy_range_internal(BdrvChild *src,
                                                     bool recurse_src)
 {
     BdrvTrackedRequest src_req, dst_req;
-    BlockDriverState *src_bs = src->bs;
-    BlockDriverState *dst_bs = dst->bs;
     int ret;
 
-    if (!src || !dst || !src->bs || !dst->bs) {
+    if (!dst || !dst->bs) {
         return -ENOMEDIUM;
     }
-    ret = bdrv_check_byte_request(src->bs, src_offset, bytes);
-    if (ret) {
-        return ret;
-    }
-
     ret = bdrv_check_byte_request(dst->bs, dst_offset, bytes);
     if (ret) {
         return ret;
@@ -2917,16 +2910,24 @@ static int coroutine_fn bdrv_co_copy_range_internal(BdrvChild *src,
         return bdrv_co_pwrite_zeroes(dst, dst_offset, bytes, flags);
     }
 
+    if (!src || !src->bs) {
+        return -ENOMEDIUM;
+    }
+    ret = bdrv_check_byte_request(src->bs, src_offset, bytes);
+    if (ret) {
+        return ret;
+    }
+
     if (!src->bs->drv->bdrv_co_copy_range_from
         || !dst->bs->drv->bdrv_co_copy_range_to
         || src->bs->encrypted || dst->bs->encrypted) {
         return -ENOTSUP;
     }
-    bdrv_inc_in_flight(src_bs);
-    bdrv_inc_in_flight(dst_bs);
-    tracked_request_begin(&src_req, src_bs, src_offset,
+    bdrv_inc_in_flight(src->bs);
+    bdrv_inc_in_flight(dst->bs);
+    tracked_request_begin(&src_req, src->bs, src_offset,
                           bytes, BDRV_TRACKED_READ);
-    tracked_request_begin(&dst_req, dst_bs, dst_offset,
+    tracked_request_begin(&dst_req, dst->bs, dst_offset,
                           bytes, BDRV_TRACKED_WRITE);
 
     wait_serialising_requests(&src_req);
@@ -2944,8 +2945,8 @@ static int coroutine_fn bdrv_co_copy_range_internal(BdrvChild *src,
     }
     tracked_request_end(&src_req);
     tracked_request_end(&dst_req);
-    bdrv_dec_in_flight(src_bs);
-    bdrv_dec_in_flight(dst_bs);
+    bdrv_dec_in_flight(src->bs);
+    bdrv_dec_in_flight(dst->bs);
     return ret;
 }
 
-- 
2.17.1

[Qemu-devel] [PATCH v4 2/3] block: Honour BDRV_REQ_NO_SERIALISING in copy range

[Fam Zheng]

This semantics is needed by drive-backup so implement it before using
this API there.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block/io.c            | 6 ++++--
 include/block/block.h | 5 +++--
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/block/io.c b/block/io.c
index b8845708d7..1a2272fad3 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2930,8 +2930,10 @@ static int coroutine_fn bdrv_co_copy_range_internal(BdrvChild *src,
     tracked_request_begin(&dst_req, dst->bs, dst_offset,
                           bytes, BDRV_TRACKED_WRITE);
 
-    wait_serialising_requests(&src_req);
-    wait_serialising_requests(&dst_req);
+    if (!(flags & BDRV_REQ_NO_SERIALISING)) {
+        wait_serialising_requests(&src_req);
+        wait_serialising_requests(&dst_req);
+    }
     if (recurse_src) {
         ret = src->bs->drv->bdrv_co_copy_range_from(src->bs,
                                                     src, src_offset,
diff --git a/include/block/block.h b/include/block/block.h
index 2ffc1c64c6..e5c7759a0c 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -659,13 +659,14 @@ void bdrv_unregister_buf(BlockDriverState *bs, void *host);
  * @dst: Destination child to copy data to
  * @dst_offset: offset in @dst image to write data
  * @bytes: number of bytes to copy
- * @flags: request flags. Must be one of:
- *         0 - actually read data from src;
+ * @flags: request flags. Supported flags:
  *         BDRV_REQ_ZERO_WRITE - treat the @src range as zero data and do zero
  *                               write on @dst as if bdrv_co_pwrite_zeroes is
  *                               called. Used to simplify caller code, or
  *                               during BlockDriver.bdrv_co_copy_range_from()
  *                               recursion.
+ *         BDRV_REQ_NO_SERIALISING - do not serialize with other overlapping
+ *                                   requests currently in flight.
  *
  * Returns: 0 if succeeded; negative error code if failed.
  **/
-- 
2.17.1

[Qemu-devel] [PATCH v4 3/3] backup: Use copy offloading

[Fam Zheng]

The implementation is similar to the 'qemu-img convert'. In the
beginning of the job, offloaded copy is attempted. If it fails, further
I/O will go through the existing bounce buffer code path.

Then, as Kevin pointed out, both this and qemu-img convert can benefit
from a local check if one request fails because of, for example, the
offset is beyond EOF, but another may well be accepted by the protocol
layer. This will be implemented separately.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block/backup.c     | 150 ++++++++++++++++++++++++++++++++-------------
 block/trace-events |   1 +
 2 files changed, 110 insertions(+), 41 deletions(-)

diff --git a/block/backup.c b/block/backup.c
index d18be40caf..81895ddbe2 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -45,6 +45,8 @@ typedef struct BackupBlockJob {
     QLIST_HEAD(, CowRequest) inflight_reqs;
 
     HBitmap *copy_bitmap;
+    bool use_copy_range;
+    int64_t copy_range_size;
 } BackupBlockJob;
 
 static const BlockJobDriver backup_job_driver;
@@ -86,19 +88,101 @@ static void cow_request_end(CowRequest *req)
     qemu_co_queue_restart_all(&req->wait_queue);
 }
 
+/* Copy range to target with a bounce buffer and return the bytes copied. If
+ * error occured, return a negative error number */
+static int coroutine_fn backup_cow_with_bounce_buffer(BackupBlockJob *job,
+                                                      int64_t start,
+                                                      int64_t end,
+                                                      bool is_write_notifier,
+                                                      bool *error_is_read,
+                                                      void **bounce_buffer)
+{
+    int ret;
+    struct iovec iov;
+    QEMUIOVector qiov;
+    BlockBackend *blk = job->common.blk;
+    int nbytes;
+
+    hbitmap_reset(job->copy_bitmap, start / job->cluster_size, 1);
+    nbytes = MIN(job->cluster_size, job->len - start);
+    if (!*bounce_buffer) {
+        *bounce_buffer = blk_blockalign(blk, job->cluster_size);
+    }
+    iov.iov_base = *bounce_buffer;
+    iov.iov_len = nbytes;
+    qemu_iovec_init_external(&qiov, &iov, 1);
+
+    ret = blk_co_preadv(blk, start, qiov.size, &qiov,
+                        is_write_notifier ? BDRV_REQ_NO_SERIALISING : 0);
+    if (ret < 0) {
+        trace_backup_do_cow_read_fail(job, start, ret);
+        if (error_is_read) {
+            *error_is_read = true;
+        }
+        goto fail;
+    }
+
+    if (qemu_iovec_is_zero(&qiov)) {
+        ret = blk_co_pwrite_zeroes(job->target, start,
+                                   qiov.size, BDRV_REQ_MAY_UNMAP);
+    } else {
+        ret = blk_co_pwritev(job->target, start,
+                             qiov.size, &qiov,
+                             job->compress ? BDRV_REQ_WRITE_COMPRESSED : 0);
+    }
+    if (ret < 0) {
+        trace_backup_do_cow_write_fail(job, start, ret);
+        if (error_is_read) {
+            *error_is_read = false;
+        }
+        goto fail;
+    }
+
+    return nbytes;
+fail:
+    hbitmap_set(job->copy_bitmap, start / job->cluster_size, 1);
+    return ret;
+
+}
+
+/* Copy range to target and return the bytes copied. If error occured, return a
+ * negative error number. */
+static int coroutine_fn backup_cow_with_offload(BackupBlockJob *job,
+                                                int64_t start,
+                                                int64_t end,
+                                                bool is_write_notifier)
+{
+    int ret;
+    int nr_clusters;
+    BlockBackend *blk = job->common.blk;
+    int nbytes;
+
+    assert(QEMU_IS_ALIGNED(job->copy_range_size, job->cluster_size));
+    nbytes = MIN(job->copy_range_size, end - start);
+    nr_clusters = DIV_ROUND_UP(nbytes, job->cluster_size);
+    hbitmap_reset(job->copy_bitmap, start / job->cluster_size,
+                  nr_clusters);
+    ret = blk_co_copy_range(blk, start, job->target, start, nbytes,
+                            is_write_notifier ? BDRV_REQ_NO_SERIALISING : 0);
+    if (ret < 0) {
+        trace_backup_do_cow_copy_range_fail(job, start, ret);
+        hbitmap_set(job->copy_bitmap, start / job->cluster_size,
+                    nr_clusters);
+        return ret;
+    }
+
+    return nbytes;
+}
+
 static int coroutine_fn backup_do_cow(BackupBlockJob *job,
                                       int64_t offset, uint64_t bytes,
                                       bool *error_is_read,
                                       bool is_write_notifier)
 {
-    BlockBackend *blk = job->common.blk;
     CowRequest cow_request;
-    struct iovec iov;
-    QEMUIOVector bounce_qiov;
-    void *bounce_buffer = NULL;
     int ret = 0;
     int64_t start, end; /* bytes */
-    int n; /* bytes */
+    void *bounce_buffer = NULL;
 
     qemu_co_rwlock_rdlock(&job->flush_rwlock);
 
@@ -110,60 +194,38 @@ static int coroutine_fn backup_do_cow(BackupBlockJob *job,
     wait_for_overlapping_requests(job, start, end);
     cow_request_begin(&cow_request, job, start, end);
 
-    for (; start < end; start += job->cluster_size) {
+    while (start < end) {
         if (!hbitmap_get(job->copy_bitmap, start / job->cluster_size)) {
             trace_backup_do_cow_skip(job, start);
+            start += job->cluster_size;
             continue; /* already copied */
         }
-        hbitmap_reset(job->copy_bitmap, start / job->cluster_size, 1);
 
         trace_backup_do_cow_process(job, start);
 
-        n = MIN(job->cluster_size, job->len - start);
-
-        if (!bounce_buffer) {
-            bounce_buffer = blk_blockalign(blk, job->cluster_size);
-        }
-        iov.iov_base = bounce_buffer;
-        iov.iov_len = n;
-        qemu_iovec_init_external(&bounce_qiov, &iov, 1);
-
-        ret = blk_co_preadv(blk, start, bounce_qiov.size, &bounce_qiov,
-                            is_write_notifier ? BDRV_REQ_NO_SERIALISING : 0);
-        if (ret < 0) {
-            trace_backup_do_cow_read_fail(job, start, ret);
-            if (error_is_read) {
-                *error_is_read = true;
+        if (job->use_copy_range) {
+            ret = backup_cow_with_offload(job, start, end, is_write_notifier);
+            if (ret < 0) {
+                job->use_copy_range = false;
             }
-            hbitmap_set(job->copy_bitmap, start / job->cluster_size, 1);
-            goto out;
         }
-
-        if (buffer_is_zero(iov.iov_base, iov.iov_len)) {
-            ret = blk_co_pwrite_zeroes(job->target, start,
-                                       bounce_qiov.size, BDRV_REQ_MAY_UNMAP);
-        } else {
-            ret = blk_co_pwritev(job->target, start,
-                                 bounce_qiov.size, &bounce_qiov,
-                                 job->compress ? BDRV_REQ_WRITE_COMPRESSED : 0);
+        if (!job->use_copy_range) {
+            ret = backup_cow_with_bounce_buffer(job, start, end, is_write_notifier,
+                                                error_is_read, &bounce_buffer);
         }
         if (ret < 0) {
-            trace_backup_do_cow_write_fail(job, start, ret);
-            if (error_is_read) {
-                *error_is_read = false;
-            }
-            hbitmap_set(job->copy_bitmap, start / job->cluster_size, 1);
-            goto out;
+            break;
         }
 
         /* Publish progress, guest I/O counts as progress too.  Note that the
          * offset field is an opaque progress value, it is not a disk offset.
          */
-        job->bytes_read += n;
-        job_progress_update(&job->common.job, n);
+        start += ret;
+        job->bytes_read += ret;
+        job_progress_update(&job->common.job, ret);
+        ret = 0;
     }
 
-out:
     if (bounce_buffer) {
         qemu_vfree(bounce_buffer);
     }
@@ -665,6 +727,12 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
     } else {
         job->cluster_size = MAX(BACKUP_CLUSTER_SIZE_DEFAULT, bdi.cluster_size);
     }
+    job->use_copy_range = true;
+    job->copy_range_size = MIN_NON_ZERO(blk_get_max_transfer(job->common.blk),
+                                        blk_get_max_transfer(job->target));
+    job->copy_range_size = MAX(job->cluster_size,
+                               QEMU_ALIGN_UP(job->copy_range_size,
+                                             job->cluster_size));
 
     /* Required permissions are already taken with target's blk_new() */
     block_job_add_bdrv(&job->common, "target", target, 0, BLK_PERM_ALL,
diff --git a/block/trace-events b/block/trace-events
index 2d59b53fd3..c35287b48a 100644
--- a/block/trace-events
+++ b/block/trace-events
@@ -42,6 +42,7 @@ backup_do_cow_skip(void *job, int64_t start) "job %p start %"PRId64
 backup_do_cow_process(void *job, int64_t start) "job %p start %"PRId64
 backup_do_cow_read_fail(void *job, int64_t start, int ret) "job %p start %"PRId64" ret %d"
 backup_do_cow_write_fail(void *job, int64_t start, int ret) "job %p start %"PRId64" ret %d"
+backup_do_cow_copy_range_fail(void *job, int64_t start, int ret) "job %p start %"PRId64" ret %d"
 
 # blockdev.c
 qmp_block_job_cancel(void *job) "job %p"
-- 
2.17.1

Re: [Qemu-devel] [PATCH v4 1/3] block: Fix parameter checking in bdrv_co_copy_range_internal

[Jeff Cody]

On Tue, Jul 03, 2018 at 10:37:56AM +0800, Fam Zheng wrote:
> src may be NULL if BDRV_REQ_ZERO_WRITE flag is set, in this case only
> check dst and dst->bs. This bug was introduced when moving in the
> request tracking code from bdrv_co_copy_range, in 37aec7d75eb.
> 
> This especially fixes the possible segfault when initializing src_bs
> with a NULL src.
> 
> Signed-off-by: Fam Zheng <famz@redhat.com>

Reviewed-by: Jeff Cody <jcody@redhat.com>

> ---
>  block/io.c | 29 +++++++++++++++--------------
>  1 file changed, 15 insertions(+), 14 deletions(-)
> 
> diff --git a/block/io.c b/block/io.c
> index 7035b78a20..b8845708d7 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -2897,18 +2897,11 @@ static int coroutine_fn bdrv_co_copy_range_internal(BdrvChild *src,
>                                                      bool recurse_src)
>  {
>      BdrvTrackedRequest src_req, dst_req;
> -    BlockDriverState *src_bs = src->bs;
> -    BlockDriverState *dst_bs = dst->bs;
>      int ret;
>  
> -    if (!src || !dst || !src->bs || !dst->bs) {
> +    if (!dst || !dst->bs) {
>          return -ENOMEDIUM;
>      }
> -    ret = bdrv_check_byte_request(src->bs, src_offset, bytes);
> -    if (ret) {
> -        return ret;
> -    }
> -
>      ret = bdrv_check_byte_request(dst->bs, dst_offset, bytes);
>      if (ret) {
>          return ret;
> @@ -2917,16 +2910,24 @@ static int coroutine_fn bdrv_co_copy_range_internal(BdrvChild *src,
>          return bdrv_co_pwrite_zeroes(dst, dst_offset, bytes, flags);
>      }
>  
> +    if (!src || !src->bs) {
> +        return -ENOMEDIUM;
> +    }
> +    ret = bdrv_check_byte_request(src->bs, src_offset, bytes);
> +    if (ret) {
> +        return ret;
> +    }
> +
>      if (!src->bs->drv->bdrv_co_copy_range_from
>          || !dst->bs->drv->bdrv_co_copy_range_to
>          || src->bs->encrypted || dst->bs->encrypted) {
>          return -ENOTSUP;
>      }
> -    bdrv_inc_in_flight(src_bs);
> -    bdrv_inc_in_flight(dst_bs);
> -    tracked_request_begin(&src_req, src_bs, src_offset,
> +    bdrv_inc_in_flight(src->bs);
> +    bdrv_inc_in_flight(dst->bs);
> +    tracked_request_begin(&src_req, src->bs, src_offset,
>                            bytes, BDRV_TRACKED_READ);
> -    tracked_request_begin(&dst_req, dst_bs, dst_offset,
> +    tracked_request_begin(&dst_req, dst->bs, dst_offset,
>                            bytes, BDRV_TRACKED_WRITE);
>  
>      wait_serialising_requests(&src_req);
> @@ -2944,8 +2945,8 @@ static int coroutine_fn bdrv_co_copy_range_internal(BdrvChild *src,
>      }
>      tracked_request_end(&src_req);
>      tracked_request_end(&dst_req);
> -    bdrv_dec_in_flight(src_bs);
> -    bdrv_dec_in_flight(dst_bs);
> +    bdrv_dec_in_flight(src->bs);
> +    bdrv_dec_in_flight(dst->bs);
>      return ret;
>  }
>  
> -- 
> 2.17.1
> 

Re: [Qemu-devel] [PATCH v4 0/3] backup: Use copy offloading

[Jeff Cody]

On Tue, Jul 03, 2018 at 10:37:55AM +0800, Fam Zheng wrote:
> v4: Rebase to master.
>     Pick up Stefan's rev-bys.
>     Include a block/io.c fix to fix a new issue caused by recent block/io.c
>     change - our drive-backup cases in iotests exposes the bug loudly.
> 
> This enhances the backup job to make use of the copy offloading API. It
> eliminates the necessity to use the bounce buffer as well as speeding up the
> copy operation when the backend supports it.
> 
> v3: Don't forget coroutine_fn. [Stefan]
>     Don't reset job->use_copy_range redundantly. [Stefan]
> 
> v2: Use helper functions. [Stefan]
> 
> Fam Zheng (3):
>   block: Fix parameter checking in bdrv_co_copy_range_internal
>   block: Honour BDRV_REQ_NO_SERIALISING in copy range
>   backup: Use copy offloading
> 
>  block/backup.c        | 150 ++++++++++++++++++++++++++++++------------
>  block/io.c            |  35 +++++-----
>  block/trace-events    |   1 +
>  include/block/block.h |   5 +-
>  4 files changed, 132 insertions(+), 59 deletions(-)
> 
> -- 
> 2.17.1
> 

Thanks,

Applied to my block branch:

git://github.com/codyprime/qemu-kvm-jtc block

-Jeff