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

[Alexander Ivanov]

On 3/14/24 13:44, Daniel P. Berrangé wrote:
> 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....
Thank you.
I think it would be better to use 'g_spawn_check_exit_status' because 
there is no
'g_spawn_check_wait_status' in glib before 2.70 and even in 2.78 it 
leads to
'g_spawn_check_wait_status is deprecated: Not available before 2.70' error.
> > +
> > +            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

--
Best regards,
Alexander Ivanov