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Re: [Qemu-block] [Qemu-devel] [PATCH v4 09/20] parallels: Switch to .bdr

From: Eric Blake
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v4 09/20] parallels: Switch to .bdrv_co_block_status()
Date: Thu, 30 Nov 2017 16:12:38 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0

On 11/30/2017 03:03 AM, Vladimir Sementsov-Ogievskiy wrote:
12.10.2017 21:59, Eric Blake wrote:
We are gradually moving away from sector-based interfaces, towards
byte-based.  Update the parallels driver accordingly.  Note that
the internal function block_status() is still sector-based, because
it is still in use by other sector-based functions; but that's okay
because request_alignment is 512 as a result of those functions.
For now, no optimizations are added based on the mapping hint.

Signed-off-by: Eric Blake <address@hidden>


+static int coroutine_fn parallels_co_block_status(BlockDriverState *bs,
+                                                  bool want_zero,
+                                                  int64_t offset,
+                                                  int64_t bytes,
+                                                  int64_t *pnum,
+                                                  int64_t *map,
+                                                  BlockDriverState **file)
      BDRVParallelsState *s = bs->opaque;
-    int64_t offset;
+    int count;

+    assert(QEMU_IS_ALIGNED(offset | bytes, BDRV_SECTOR_SIZE));
-    offset = block_status(s, sector_num, nb_sectors, pnum);
+    offset = block_status(s, offset >> BDRV_SECTOR_BITS,
+                          bytes >> BDRV_SECTOR_BITS, &count);

      if (offset < 0) {

pnum=count*BDRV_SECTOR_SIZE and map=0 setting missed here.

          return 0;

Setting *map is only required when return value includes BDRV_BLOCK_OFFSET_VALID, so that one was not necessary. But you do raise an interesting point about a pre-existing bug with pnum not being set. Commit 298a1665a guarantees that *pnum is 0 (and not uninitialized garbage) - but that still violates the contract that we (want to) have that all drivers either make progress or return an error (setting pnum to 0 should only be done at EOF or on error).

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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