Re: [PATCH v2] block: Use LVM tools for LV block device truncation

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Mar 13, 2024 at 11:43:27AM +0100, Alexander Ivanov wrote:
> If a block device is an LVM logical volume we can resize it using
> standard LVM tools.
> 
> Add a helper to detect if a device is a DM device. In raw_co_truncate()
> check if the block device is DM and resize it executing lvresize.
> 
> Signed-off-by: Alexander Ivanov <alexander.ivanov@virtuozzo.com>
> ---
>  block/file-posix.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 61 insertions(+)
> 
> diff --git a/block/file-posix.c b/block/file-posix.c
> index 35684f7e21..5f07d98aa5 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -2642,6 +2642,38 @@ raw_regular_truncate(BlockDriverState *bs, int fd, int64_t offset,
>      return raw_thread_pool_submit(handle_aiocb_truncate, &acb);
>  }

>  static int coroutine_fn raw_co_truncate(BlockDriverState *bs, int64_t offset,
>                                          bool exact, PreallocMode prealloc,
>                                          BdrvRequestFlags flags, Error **errp)
> @@ -2670,6 +2702,35 @@ static int coroutine_fn raw_co_truncate(BlockDriverState *bs, int64_t offset,
>      if (S_ISCHR(st.st_mode) || S_ISBLK(st.st_mode)) {
>          int64_t cur_length = raw_getlength(bs);
>  
> +        /*
> +         * Try to resize an LVM device using LVM tools.
> +         */
> +        if (device_is_dm(&st) && offset > 0) {
> +            int spawn_flags = G_SPAWN_SEARCH_PATH | G_SPAWN_STDOUT_TO_DEV_NULL;
> +            int status;
> +            bool success;
> +            char *err;
> +            GError *gerr = NULL;
> +            g_autofree char *size_str = g_strdup_printf("%ldB", offset);

offset is 64-bit, but '%ld' is not guaranteed to be 64-bit. I expect
this will break on 32-bit platforms. Try PRId64 instead.

> +            const char *cmd[] = {"lvresize", "-f", "-L",
> +                                 size_str, bs->filename, NULL};
> +
> +            success = g_spawn_sync(NULL, (gchar **)cmd, NULL, spawn_flags,
> +                                   NULL, NULL, NULL, &err, &status, &gerr);
> +
> +            if (success && WEXITSTATUS(status) == 0) {
> +                return 0;
> +            }

We should probably check  'g_spawn_check_wait_status' rather than
WEXITSTATUS, as this then gives us further eror message details
that....

> +
> +            if (!success) {
> +                error_setg(errp, "lvresize execution error: %s", gerr->message);
> +            } else {
> +                error_setg(errp, "%s", err);

...we would also include here, such as the exit code or terminal
signal.

> +            }
> +
> +            return -EINVAL;
> +        }
> +
>          if (offset != cur_length && exact) {
>              error_setg(errp, "Cannot resize device files");
>              return -ENOTSUP;
> -- 
> 2.40.1
> 
> 

With regards,
Daniel
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