Commit ceaca56f authored by Max Reitz's avatar Max Reitz
Browse files

block: Add bdrv_has_zero_init_truncate() 



No .bdrv_has_zero_init() implementation returns 1 if growing the file
would add non-zero areas (at least with PREALLOC_MODE_OFF), so using it
in lieu of this new function was always safe.

But on the other hand, it is possible that growing an image that is not
zero-initialized would still add a zero-initialized area, like when
using nonpreallocating truncation on a preallocated image.  For callers
that care only about truncation, not about creation with potential
preallocation, this new function is useful.

Alternatively, we could have added a PreallocMode parameter to
bdrv_has_zero_init().  But the only user would have been qemu-img
convert, which does not have a plain PreallocMode value right now -- it
would have to parse the creation option to obtain it.  Therefore, the
simpler solution is to let bdrv_has_zero_init() inquire the
preallocation status and add the new bdrv_has_zero_init_truncate() that
presupposes PREALLOC_MODE_OFF.

Signed-off-by: default avatarMax Reitz <mreitz@redhat.com>
Message-id: 20190724171239.8764-4-mreitz@redhat.com
Reviewed-by: default avatarMaxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: default avatarStefano Garzarella <sgarzare@redhat.com>
Signed-off-by: default avatarMax Reitz <mreitz@redhat.com>
parent cdf3bc93

block.c

+21 −0
Original line number Diff line number Diff line
@@ -5078,6 +5078,27 @@ int bdrv_has_zero_init(BlockDriverState *bs) 
    return 0;

}



int bdrv_has_zero_init_truncate(BlockDriverState *bs)

{

    if (!bs->drv) {

        return 0;

    }



    if (bs->backing) {

        /* Depends on the backing image length, but better safe than sorry */

        return 0;

    }

    if (bs->drv->bdrv_has_zero_init_truncate) {

        return bs->drv->bdrv_has_zero_init_truncate(bs);

    }

    if (bs->file && bs->drv->is_filter) {

        return bdrv_has_zero_init_truncate(bs->file->bs);

    }



    /* safe default */

    return 0;

}



bool bdrv_unallocated_blocks_are_zero(BlockDriverState *bs)

{

    BlockDriverInfo bdi;

include/block/block.h

+1 −0
Original line number Diff line number Diff line
@@ -443,6 +443,7 @@ int bdrv_pdiscard(BdrvChild *child, int64_t offset, int64_t bytes); 
int bdrv_co_pdiscard(BdrvChild *child, int64_t offset, int64_t bytes);

int bdrv_has_zero_init_1(BlockDriverState *bs);

int bdrv_has_zero_init(BlockDriverState *bs);

int bdrv_has_zero_init_truncate(BlockDriverState *bs);

bool bdrv_unallocated_blocks_are_zero(BlockDriverState *bs);

bool bdrv_can_write_zeroes_with_unmap(BlockDriverState *bs);

int bdrv_block_status(BlockDriverState *bs, int64_t offset,

include/block/block_int.h

+7 −0
Original line number Diff line number Diff line
@@ -419,9 +419,16 @@ struct BlockDriver { 
    /*

     * Returns 1 if newly created images are guaranteed to contain only

     * zeros, 0 otherwise.

     * Must return 0 if .bdrv_has_zero_init_truncate() returns 0.

     */

    int (*bdrv_has_zero_init)(BlockDriverState *bs);



    /*

     * Returns 1 if new areas added by growing the image with

     * PREALLOC_MODE_OFF contain only zeros, 0 otherwise.

     */

    int (*bdrv_has_zero_init_truncate)(BlockDriverState *bs);



    /* Remove fd handlers, timers, and other event loop callbacks so the event

     * loop is no longer in use.  Called with no in-flight requests and in

     * depth-first traversal order with parents before child nodes.