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Re: [Qemu-block] [PATCH 6/8] block: Let format drivers pass @exact
From: |
Maxim Levitsky |
Subject: |
Re: [Qemu-block] [PATCH 6/8] block: Let format drivers pass @exact |
Date: |
Wed, 18 Sep 2019 23:51:48 +0300 |
On Wed, 2019-09-18 at 11:51 +0200, Max Reitz wrote:
> When truncating a format node, the @exact parameter is generally handled
> simply by virtue of the format storing the new size in the image
> metadata. Such formats do not need to pass on the parameter to their
> file nodes.
>
> There are exceptions, though:
> - raw and crypto cannot store the image size, and thus must pass on
> @exact.
>
> - When using qcow2 with an external data file, it just makes sense to
> keep its size in sync with the qcow2 virtual disk (because the
> external data file is the virtual disk). Therefore, we should pass
> @exact when truncating it.
>
> Signed-off-by: Max Reitz <address@hidden>
> ---
> block/crypto.c | 2 +-
> block/qcow2.c | 15 ++++++++++++++-
> block/raw-format.c | 2 +-
> 3 files changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/block/crypto.c b/block/crypto.c
> index e5a1a2cdf3..24823835c1 100644
> --- a/block/crypto.c
> +++ b/block/crypto.c
> @@ -311,7 +311,7 @@ block_crypto_co_truncate(BlockDriverState *bs, int64_t
> offset, bool exact,
>
> offset += payload_offset;
>
> - return bdrv_co_truncate(bs->file, offset, false, prealloc, errp);
> + return bdrv_co_truncate(bs->file, offset, exact, prealloc, errp);
> }
>
> static void block_crypto_close(BlockDriverState *bs)
> diff --git a/block/qcow2.c b/block/qcow2.c
> index 157b9b75d9..4ef19dd29a 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -3822,6 +3822,13 @@ static int coroutine_fn
> qcow2_co_truncate(BlockDriverState *bs, int64_t offset,
> if ((last_cluster + 1) * s->cluster_size < old_file_size) {
> Error *local_err = NULL;
>
> + /*
> + * Do not pass @exact here: It will not help the user if
> + * we get an error here just because they wanted to shrink
> + * their qcow2 image (on a block device) with qemu-img.
> + * (And on the qcow2 layer, the @exact requirement is
> + * always fulfilled, so there is no need to pass it on.)
> + */
> bdrv_co_truncate(bs->file, (last_cluster + 1) * s->cluster_size,
> false, PREALLOC_MODE_OFF, &local_err);
> if (local_err) {
> @@ -3840,7 +3847,12 @@ static int coroutine_fn
> qcow2_co_truncate(BlockDriverState *bs, int64_t offset,
> switch (prealloc) {
> case PREALLOC_MODE_OFF:
> if (has_data_file(bs)) {
> - ret = bdrv_co_truncate(s->data_file, offset, false, prealloc,
> errp);
> + /*
> + * If the caller wants an exact resize, the external data
> + * file should be resized to the exact target size, too,
> + * so we pass @exact here.
> + */
> + ret = bdrv_co_truncate(s->data_file, offset, exact, prealloc,
> errp);
> if (ret < 0) {
> goto fail;
> }
> @@ -3925,6 +3937,7 @@ static int coroutine_fn
> qcow2_co_truncate(BlockDriverState *bs, int64_t offset,
> /* Allocate the data area */
> new_file_size = allocation_start +
> nb_new_data_clusters * s->cluster_size;
> + /* Image file grows, so @exact does not matter */
> ret = bdrv_co_truncate(bs->file, new_file_size, false, prealloc,
> errp);
>
> if (ret < 0) {
> error_prepend(errp, "Failed to resize underlying file: ");
> diff --git a/block/raw-format.c b/block/raw-format.c
> index 57d84d0bae..3a76ec7dd2 100644
> --- a/block/raw-format.c
> +++ b/block/raw-format.c
> @@ -387,7 +387,7 @@ static int coroutine_fn raw_co_truncate(BlockDriverState
> *bs, int64_t offset,
>
> s->size = offset;
> offset += s->offset;
> - return bdrv_co_truncate(bs->file, offset, false, prealloc, errp);
> + return bdrv_co_truncate(bs->file, offset, exact, prealloc, errp);
> }
>
> static void raw_eject(BlockDriverState *bs, bool eject_flag)
Looks all right.
Reviewed-by: Maxim Levitsky <address@hidden>
Best regards,
Maxim Levitsky
- Re: [Qemu-block] [PATCH 1/8] block: Handle filter truncation like native impl., (continued)
- [Qemu-block] [PATCH 2/8] block/cor: Drop cor_co_truncate(), Max Reitz, 2019/09/18
- [Qemu-block] [PATCH 3/8] block: Do not truncate file node when formatting, Max Reitz, 2019/09/18
- [Qemu-block] [PATCH 5/8] block: Evaluate @exact in protocol drivers, Max Reitz, 2019/09/18
- [Qemu-block] [PATCH 4/8] block: Add @exact parameter to bdrv_co_truncate(), Max Reitz, 2019/09/18
- [Qemu-block] [PATCH 6/8] block: Let format drivers pass @exact, Max Reitz, 2019/09/18
- Re: [Qemu-block] [PATCH 6/8] block: Let format drivers pass @exact,
Maxim Levitsky <=
- [Qemu-block] [PATCH 7/8] block: Pass truncate exact=true where reasonable, Max Reitz, 2019/09/18
- [Qemu-block] [PATCH 8/8] Revert "qemu-img: Check post-truncation size", Max Reitz, 2019/09/18