Re: [PATCH v12 10/14] block: include supported_read_flags into BDS structure

[Vladimir Sementsov-Ogievskiy]

22.10.2020 21:13, Andrey Shinkevich wrote:

Add the new member supported_read_flags to the BlockDriverState
structure. It will control the flags set for copy-on-read operations.
Make the block generic layer evaluate supported read flags before they
go to a block driver.

Suggested-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
Signed-off-by: Andrey Shinkevich <andrey.shinkev...@virtuozzo.com>
---
  block/io.c                | 12 ++++++++++--
  include/block/block_int.h |  4 ++++
  2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/block/io.c b/block/io.c
index 54f0968..78ddf13 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1392,6 +1392,9 @@ static int coroutine_fn bdrv_aligned_preadv(BdrvChild 
*child,
      if (flags & BDRV_REQ_COPY_ON_READ) {
          int64_t pnum;

+ /* The flag BDRV_REQ_COPY_ON_READ has reached its addressee */

+        flags &= ~BDRV_REQ_COPY_ON_READ;
+
          ret = bdrv_is_allocated(bs, offset, bytes, &pnum);
          if (ret < 0) {
              goto out;
@@ -1413,9 +1416,13 @@ static int coroutine_fn bdrv_aligned_preadv(BdrvChild 
*child,
          goto out;
      }

+ if (flags & ~bs->supported_read_flags) {

+        abort();
+    }
+

So, you decided to be strict with all read-flags passed to driver, not only 
PREFETCH.. It makes sense.

      max_bytes = ROUND_UP(MAX(0, total_bytes - offset), align);
      if (bytes <= max_bytes && bytes <= max_transfer) {
-        ret = bdrv_driver_preadv(bs, offset, bytes, qiov, qiov_offset, 0);
+        ret = bdrv_driver_preadv(bs, offset, bytes, qiov, qiov_offset, flags);
          goto out;
      }

@@ -1428,7 +1435,8 @@ static int coroutine_fn bdrv_aligned_preadv(BdrvChild *child, ret = bdrv_driver_preadv(bs, offset + bytes - bytes_remaining,

                                       num, qiov,
-                                     qiov_offset + bytes - bytes_remaining, 0);
+                                     qiov_offset + bytes - bytes_remaining,
+                                     flags);
              max_bytes -= num;
          } else {
              num = bytes_remaining;
diff --git a/include/block/block_int.h b/include/block/block_int.h
index f782737..474174c 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -873,6 +873,10 @@ struct BlockDriverState {
      /* I/O Limits */
      BlockLimits bl;

+ /*

+     * Flags honored during pread
+     */
+    unsigned int supported_read_flags;
      /* Flags honored during pwrite (so far: BDRV_REQ_FUA,
       * BDRV_REQ_WRITE_UNCHANGED).
       * If a driver does not support BDRV_REQ_WRITE_UNCHANGED, those

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>

--
Best regards,
Vladimir