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block: add enable_write_cache flag 

Add a enable_write_cache flag in the block driver state, and use it to
decide if we claim to have a volatile write cache that needs controlled
flushing from the guest.  The flag is off if cache=writethrough is
defined because O_DSYNC guarantees that every write goes to stable
storage, and it is on for cache=none and cache=writeback.

Both scsi-disk and ide now use the new flage, changing from their
defaults of always off (ide) or always on (scsi-disk).

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
This commit is contained in:
Christoph Hellwig 2009-09-04 19:01:15 +02:00 committed by Anthony Liguori
parent b8193adbda
commit e900a7b748
5 changed files with 27 additions and 3 deletions
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15
block.c
View File

@ -408,6 +408,16 @@ int bdrv_open2(BlockDriverState *bs, const char *filename, int flags,
}
bs->drv = drv;
bs->opaque = qemu_mallocz(drv->instance_size);
/*
* Yes, BDRV_O_NOCACHE aka O_DIRECT means we have to present a
* write cache to the guest. We do need the fdatasync to flush
* out transactions for block allocations, and we maybe have a
* volatile write cache in our backing device to deal with.
*/
if (flags & (BDRV_O_CACHE_WB|BDRV_O_NOCACHE))
bs->enable_write_cache = 1;
/* Note: for compatibility, we open disk image files as RDWR, and
RDONLY as fallback */
if (!(flags & BDRV_O_FILE))
@ -918,6 +928,11 @@ int bdrv_is_sg(BlockDriverState *bs)
return bs->sg;
}
int bdrv_enable_write_cache(BlockDriverState *bs)
{
return bs->enable_write_cache;
}
/* XXX: no longer used */
void bdrv_set_change_cb(BlockDriverState *bs,
void (*change_cb)(void *opaque), void *opaque)

1
block.h
View File

@ -135,6 +135,7 @@ int bdrv_get_translation_hint(BlockDriverState *bs);
int bdrv_is_removable(BlockDriverState *bs);
int bdrv_is_read_only(BlockDriverState *bs);
int bdrv_is_sg(BlockDriverState *bs);
int bdrv_enable_write_cache(BlockDriverState *bs);
int bdrv_is_inserted(BlockDriverState *bs);
int bdrv_media_changed(BlockDriverState *bs);
int bdrv_is_locked(BlockDriverState *bs);

3
block_int.h
View File

@ -158,6 +158,9 @@ struct BlockDriverState {
/* the memory alignment required for the buffers handled by this driver */
int buffer_alignment;
/* do we need to tell the quest if we have a volatile write cache? */
int enable_write_cache;
/* NOTE: the following infos are only hints for real hardware
drivers. They are not used by the block driver */
int cyls, heads, secs, translation;

7
hw/ide/core.c
View File

@ -148,8 +148,11 @@ static void ide_identify(IDEState *s)
put_le16(p + 83, (1 << 14) | (1 << 13) | (1 <<12) | (1 << 10));
/* 14=set to 1, 1=SMART self test, 0=SMART error logging */
put_le16(p + 84, (1 << 14) | 0);
/* 14 = NOP supported, 0=SMART feature set enabled */
put_le16(p + 85, (1 << 14) | 1);
/* 14 = NOP supported, 5=WCACHE enabled, 0=SMART feature set enabled */
if (bdrv_enable_write_cache(s->bs))
put_le16(p + 85, (1 << 14) | (1 << 5) | 1);
else
put_le16(p + 85, (1 << 14) | 1);
/* 13=flush_cache_ext,12=flush_cache,10=lba48 */
put_le16(p + 86, (1 << 14) | (1 << 13) | (1 <<12) | (1 << 10));
/* 14=set to 1, 1=smart self test, 0=smart error logging */

4
hw/scsi-disk.c
View File

@ -709,7 +709,9 @@ static int32_t scsi_send_command(SCSIDevice *d, uint32_t tag,
memset(p,0,20);
p[0] = 8;
p[1] = 0x12;
p[2] = 4; /* WCE */
if (bdrv_enable_write_cache(s->dinfo->bdrv)) {
p[2] = 4; /* WCE */
}
p += 20;
}
if ((page == 0x3f || page == 0x2a)