Re: [PATCH v3] block: Use LVM tools for LV block device truncation

[Daniel P . Berrangé]

On Fri, Mar 15, 2024 at 09:58:38AM +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(+)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


> 
> diff --git a/block/file-posix.c b/block/file-posix.c
> index 35684f7e21..af17a43fe9 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 bool device_is_dm(struct stat *st)
> +{
> +    unsigned int maj, maj2;
> +    char line[32], devname[16];
> +    bool ret = false;
> +    FILE *f;
> +
> +    if (!S_ISBLK(st->st_mode)) {
> +        return false;
> +    }
> +
> +    f = fopen("/proc/devices", "r");
> +    if (!f) {
> +        return false;
> +    }
> +
> +    maj = major(st->st_rdev);
> +
> +    while (fgets(line, sizeof(line), f)) {
> +        if (sscanf(line, "%u %15s", &maj2, devname) != 2) {
> +            continue;
> +        }
> +        if (strcmp(devname, "device-mapper") == 0) {
> +            ret = (maj == maj2);
> +            break;
> +        }
> +    }
> +
> +    fclose(f);
> +    return ret;
> +}
> +
>  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, *gerr_exit = NULL;
> +            g_autofree char *size_str = g_strdup_printf("%" PRId64 "B", 
> offset);
> +            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 && g_spawn_check_exit_status(status, &gerr_exit)) {
> +                return 0;
> +            }
> +
> +            if (success) {
> +                error_setg(errp, "%s: %s", gerr_exit->message, err);
> +            } else {
> +                error_setg(errp, "lvresize execution error: %s", 
> gerr->message);
> +            }
> +
> +            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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