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From: | Anthony Liguori |
Subject: | Re: [Qemu-devel] [PATCH] Disable O_DIRECT for physical CDROM/DVD drives |
Date: | Tue, 20 Jul 2010 12:57:55 -0500 |
User-agent: | Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.10) Gecko/20100528 Lightning/1.0b1 Thunderbird/3.0.5 |
On 07/20/2010 11:45 AM, Natalia Portillo wrote:
El 20/07/2010, a las 16:17, address@hidden escribió:From: Jes Sorensen<address@hidden> O_DIRECT (cache=none) requires sector alignment, however the physical sector size of CDROM/DVD drives is 2048, as opposed to most disk devices which use 512. QEMU is hard coding 512 all over the place, so allowing O_DIRECT for CDROM/DVD devices does not work.What about if the device is a 4096 byte/sector hard disk, a 512 byte/sector CD-ROM (IRIX ones), a 2048 byte/sector magnetooptical?
BlockDriverStates need to handle non-aligned reads/writes. As I mentioned earlier, we need cdrom_pread/cdrom_pwrite functions that do RMWs as necessary.
Regards, Anthony Liguori
We should get rid of that hard codes and use real values.Signed-off-by: Jes Sorensen<address@hidden> --- block/raw-posix.c | 5 +++++ 1 files changed, 5 insertions(+), 0 deletions(-) diff --git a/block/raw-posix.c b/block/raw-posix.c index 291699f..0ea79b6 100644 --- a/block/raw-posix.c +++ b/block/raw-posix.c @@ -1139,6 +1139,11 @@ static int cdrom_open(BlockDriverState *bs, const char *filename, int flags) BDRVRawState *s = bs->opaque; s->type = FTYPE_CD; + if (flags& BDRV_O_NOCACHE) { + fprintf(stderr, "Disabling unsupported O_DIRECT (cache=none) for " + "CDROM/DVD device (%s)\n", filename); + flags&= ~BDRV_O_NOCACHE; + } /* open will not fail even if no CD is inserted, so add O_NONBLOCK */ return raw_open_common(bs, filename, flags, O_NONBLOCK); -- 1.7.1.1
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