Commit e900a7b7 authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Anthony Liguori
Browse files

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: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarAnthony Liguori <aliguori@us.ibm.com>
parent b8193adb

block.c

+15 −0
Original line number Diff line number Diff line
@@ -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)

block.h

+1 −0
Original line number Diff line number Diff line
@@ -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);

block_int.h

+3 −0
Original line number Diff line number Diff line
@@ -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;

hw/ide/core.c

+5 −2
Original line number Diff line number Diff line
@@ -148,7 +148,10 @@ 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 */

    /* 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));

hw/scsi-disk.c

+3 −1
Original line number Diff line number Diff line
@@ -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;

                if (bdrv_enable_write_cache(s->dinfo->bdrv)) {

                     p[2] = 4; /* WCE */

                }

                p += 20;

            }

            if ((page == 0x3f || page == 0x2a)