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Date: Mon, 19 Apr 2010 15:26:06 +0100
Message-ID: <j2mfbd9d3991004190726z2e1126c4w5505a1691f16eba0@mail.gmail.com>
Subject: Re: [Qemu-devel] Re: [PATCH 2/2] block: Cache total_sectors to reduce
	bdrv_getlength calls
From: Stefan Hajnoczi <stefanha@gmail.com>
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To: Kevin Wolf <kwolf@redhat.com>
Cc: Jan Kiszka <jan.kiszka@siemens.com>, Christoph Hellwig <hch@lst.de>, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>, qemu-devel@nongnu.org

On Mon, Apr 19, 2010 at 3:10 PM, Kevin Wolf <kwolf@redhat.com> wrote:
>> @@ -416,9 +417,7 @@ static int bdrv_open_common(BlockDriverState *bs, co=
nst char *filename,
>> =A0 =A0 =A0}
>>
>> =A0 =A0 =A0bs->keep_read_only =3D bs->read_only =3D !(open_flags & BDRV_=
O_RDWR);
>> - =A0 =A0if (drv->bdrv_getlength) {
>> - =A0 =A0 =A0 =A0bs->total_sectors =3D bdrv_getlength(bs) >> BDRV_SECTOR=
_BITS;
>> - =A0 =A0}
>> + =A0 =A0bs->total_sectors =3D bdrv_getlength(bs) >> BDRV_SECTOR_BITS;
>
> Does this hunk make a difference? If drv->bdrv_getlength =3D=3D NULL, we'=
ll
> just get back the current value.

The if statement could be left as is.  I removed it to reduce the
number of places where if (drv->bdrv_getlength) is explicitly checked.
 If callers don't know the internals of bdrv_getlength() then it is
easier to extend it without auditing and changing callers.

Having said that, I did add an if (drv->bdrv_getlength) check into
bdrv_truncate...

> But now that you sent this hunk for review, one thing about the existing
> code: We should probably check the return value of bdrv_getlength.

You're right.

I'll clean this up and send a v2.

Stefan