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Re: [Qemu-devel] Re: [PATCH 2/2] block: Cache total_sectors to reduce bd
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] Re: [PATCH 2/2] block: Cache total_sectors to reduce bdrv_getlength calls |
Date: |
Mon, 19 Apr 2010 15:26:06 +0100 |
On Mon, Apr 19, 2010 at 3:10 PM, Kevin Wolf <address@hidden> wrote:
>> @@ -416,9 +417,7 @@ static int bdrv_open_common(BlockDriverState *bs, const
>> char *filename,
>> }
>>
>> bs->keep_read_only = bs->read_only = !(open_flags & BDRV_O_RDWR);
>> - if (drv->bdrv_getlength) {
>> - bs->total_sectors = bdrv_getlength(bs) >> BDRV_SECTOR_BITS;
>> - }
>> + bs->total_sectors = bdrv_getlength(bs) >> BDRV_SECTOR_BITS;
>
> Does this hunk make a difference? If drv->bdrv_getlength == 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