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Re: [Qemu-devel] [PATCH/RFC] block: Ensure that block size constraints a
From: |
Heinz Graalfs |
Subject: |
Re: [Qemu-devel] [PATCH/RFC] block: Ensure that block size constraints are considered |
Date: |
Tue, 11 Dec 2012 14:53:37 +0100 |
On Tue, 2012-12-11 at 11:30 +0100, Kevin Wolf wrote:
> Am 11.12.2012 10:58, schrieb Heinz Graalfs:
> > Hi Kevin,
> >
> > I'm using the bdrv_pread() function during boot partition detection ...
> >
> > In detail:
> > bdrv_pread() is called to read 32 bytes from a 2048 bytes formatted
> > disk. This results in setting up a read of 512 bytes (1 sector
> > multiplied by 512 current code in paio_submit()), which is wrong for a
> > O_DIRECT opened file, and produces the error.
>
> So this sounds like the real problem: bdrv_pread/pwrite assume 512 byte
> sectors. May it's better to fix it there instead of just fixing one code
> path in one backend.
>
> In any case this patch as submitted is wrong as it overflows the buffer
> passed to paio_submit. Test it with this patch:
>
> --- a/qemu-io.c
> +++ b/qemu-io.c
> @@ -1718,6 +1718,8 @@ static int openfile(char *name, int flags, int
> growable)
> bs = NULL;
> return 1;
> }
> +
> + bdrv_set_buffer_alignment(bs, 4096);
> }
>
> return 0;
>
>
> $ ./qemu-io -n -c 'read -p 0 512' /tmp/foo
> read 512/512 bytes at offset 0
> 512 bytes, 1 ops; 0.0001 sec (3.727 MiB/sec and 7633.5878 ops/sec)
> *** glibc detected *** ./qemu-io: double free or corruption (out):
> 0x00007fa22349b000 ***
>
> Kevin
>
Kevin, I tried your fix and it solves the free error...
Here is what I get:
# lsdasd
Bus-ID Status Name Device Type BlkSz Size Blocks
==============================================================================
0.0.37a1 active dasdb 94:4 ECKD 2048 6162MB 3155355
0.0.37a0 active dasdc 94:8 ECKD 512 3594MB 7362495
# ./qemu-io -c 'read -p 0 512' /dev/disk/by-path/ccw-0.0.37a0
read 512/512 bytes at offset 0
512 bytes, 1 ops; 0.0000 sec (7.512 MiB/sec and 15384.6154 ops/sec)
# ./qemu-io -n -c 'read -p 0 512' /dev/disk/by-path/ccw-0.0.37a0
read 512/512 bytes at offset 0
512 bytes, 1 ops; 0.0005 sec (904.159 KiB/sec and 1808.3183 ops/sec)
# ./qemu-io -c 'read -p 0 512' /dev/disk/by-path/ccw-0.0.37a1
read 512/512 bytes at offset 0
512 bytes, 1 ops; 0.0000 sec (7.288 MiB/sec and 14925.3731 ops/sec)
# ./qemu-io -n -c 'read -p 0 512' /dev/disk/by-path/ccw-0.0.37a1
read failed: Invalid argument
#
Are you going to fix the rest in bdrv_pread/pwrite too?
Heinz