From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:36487) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ddidM-0003qY-H7 for qemu-devel@nongnu.org; Fri, 04 Aug 2017 15:51:45 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ddidL-0006iY-BU for qemu-devel@nongnu.org; Fri, 04 Aug 2017 15:51:44 -0400 References: <1501597152-25342-1-git-send-email-anton.nefedov@virtuozzo.com> <1501597152-25342-4-git-send-email-anton.nefedov@virtuozzo.com> From: Eric Blake Message-ID: Date: Fri, 4 Aug 2017 14:51:34 -0500 MIME-Version: 1.0 In-Reply-To: <1501597152-25342-4-git-send-email-anton.nefedov@virtuozzo.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="IcpS0gnEwlnTdm8DR2l5WltaX0JS0rHxT" Subject: Re: [Qemu-devel] [PATCH v4 03/15] block: introduce BDRV_REQ_ALLOCATE flag List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anton Nefedov , qemu-devel@nongnu.org Cc: qemu-block@nongnu.org, den@virtuozzo.com, kwolf@redhat.com, mreitz@redhat.com This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --IcpS0gnEwlnTdm8DR2l5WltaX0JS0rHxT From: Eric Blake To: Anton Nefedov , qemu-devel@nongnu.org Cc: qemu-block@nongnu.org, den@virtuozzo.com, kwolf@redhat.com, mreitz@redhat.com Message-ID: Subject: Re: [PATCH v4 03/15] block: introduce BDRV_REQ_ALLOCATE flag References: <1501597152-25342-1-git-send-email-anton.nefedov@virtuozzo.com> <1501597152-25342-4-git-send-email-anton.nefedov@virtuozzo.com> In-Reply-To: <1501597152-25342-4-git-send-email-anton.nefedov@virtuozzo.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 08/01/2017 09:19 AM, Anton Nefedov wrote: > The flag is supposed to indicate that the region of the disk image has > to be sufficiently allocated so it reads as zeroes. The call with the f= lag > set has to return -ENOTSUP if allocation cannot be done efficiently > (i.e. without falling back to writing actual buffers) >=20 > Signed-off-by: Anton Nefedov > --- > include/block/block.h | 6 +++++- > include/block/block_int.h | 2 +- > block/io.c | 20 +++++++++++++++++--- > 3 files changed, 23 insertions(+), 5 deletions(-) Reviewed-by: Eric Blake You might want the commit message to be a bit more verbose... >=20 > diff --git a/include/block/block.h b/include/block/block.h > index 7fe0125..828da67 100644 > --- a/include/block/block.h > +++ b/include/block/block.h > @@ -65,9 +65,13 @@ typedef enum { > BDRV_REQ_NO_SERIALISING =3D 0x8, > BDRV_REQ_FUA =3D 0x10, > BDRV_REQ_WRITE_COMPRESSED =3D 0x20, > + /* The BDRV_REQ_ALLOCATE flag is used to indicate that the driver = has to > + * efficiently allocate the space so it reads as zeroes, or return= an error. > + */ > + BDRV_REQ_ALLOCATE =3D 0x40, > =20 > /* Mask of valid flags */ > - BDRV_REQ_MASK =3D 0x3f, > + BDRV_REQ_MASK =3D 0x7f, > } BdrvRequestFlags; > =20 > typedef struct BlockSizes { > diff --git a/include/block/block_int.h b/include/block/block_int.h > index 9b94b32..9b64411 100644 > --- a/include/block/block_int.h > +++ b/include/block/block_int.h > @@ -585,7 +585,7 @@ struct BlockDriverState { > /* Flags honored during pwrite (so far: BDRV_REQ_FUA) */ > unsigned int supported_write_flags; > /* Flags honored during pwrite_zeroes (so far: BDRV_REQ_FUA, > - * BDRV_REQ_MAY_UNMAP) */ > + * BDRV_REQ_MAY_UNMAP, BDRV_REQ_ALLOCATE) */ > unsigned int supported_zero_flags; =2E..in addition to adding the new flag here and documenting its semantic= s for drivers... > =20 > /* the following member gives a name to every node on the bs graph= =2E */ > diff --git a/block/io.c b/block/io.c > index 375fc66..04d495e 100644 > --- a/block/io.c > +++ b/block/io.c > @@ -1245,7 +1245,7 @@ static int coroutine_fn bdrv_co_do_pwrite_zeroes(= BlockDriverState *bs, > assert(!bs->supported_zero_flags); > } > =20 > - if (ret =3D=3D -ENOTSUP) { > + if (ret =3D=3D -ENOTSUP && !(flags & BDRV_REQ_ALLOCATE)) { > /* Fall back to bounce buffer if write zeroes is unsupport= ed */ > BdrvRequestFlags write_flags =3D flags & ~BDRV_REQ_ZERO_WR= ITE; =2E..you also made sure that anywhere the flag is in use you avoid a slow= fallback... > @@ -1639,6 +1645,14 @@ int coroutine_fn bdrv_co_pwrite_zeroes(BdrvChild= *child, int64_t offset, > { > trace_bdrv_co_pwrite_zeroes(child->bs, offset, bytes, flags); > =20 > + assert(!(flags & BDRV_REQ_MAY_UNMAP && flags & BDRV_REQ_ALLOCATE))= ; > + > + if (flags & BDRV_REQ_ALLOCATE && > + !(child->bs->supported_zero_flags & BDRV_REQ_ALLOCATE)) > + { > + return -ENOTSUP; =2E..as well as providing a sane default to make the flag always trigger -ENOTSUP until individual drivers implement something in later patches. --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org --IcpS0gnEwlnTdm8DR2l5WltaX0JS0rHxT Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Comment: Public key at http://people.redhat.com/eblake/eblake.gpg Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEzBAEBCAAdFiEEccLMIrHEYCkn0vOqp6FrSiUnQ2oFAlmE0EYACgkQp6FrSiUn Q2r3vwf/dGOvKDV1/TSc+Xg+XaFUJewBecPlwjmCXGJxFmSIiSQP+hCjFUMRO1S6 Q+m2Pexr/8R75Ts0+uzv0YyeoND6MYXg9ABHvQH1Al2ylrzBwOJTSP5A0Xs/E7nB efMyXBU1D8mfOk0qIa5vbnID1QUeAN3QAmQ/P0w6vUBoNFD+ZFSkc/m+/kZ2t3U1 88OZW8dJEz1TQZcxxEuSxYfPSWP/935CqckjFwmJyoAj86z6lsfFtVLy2dWCIHR2 WdIeL693E8aTgawQBsGgTQ6M5ZGy8VhLqjHxvumZ2M0CWCGo6QTwbN+N4yx6u8od f+296sWxH76RVW13u9Rwynm7Uo7AeQ== =vowC -----END PGP SIGNATURE----- --IcpS0gnEwlnTdm8DR2l5WltaX0JS0rHxT--