[Libguestfs] [PATCH] filesystems: fix size reporting for filesystems

[Richard W.M. Jones]

On Wed, Feb 26, 2020 at 05:15:06PM +0100, Pino Toscano wrote:
> The current way to get the size of a filesystem is to query the size in
> bytes of the device. However, this gives the whole size of the device
> where a filesystem is stored, and it does not consider the actual size
> for which the filesystem is configured (e.g. in case it was shrunk).
> A simple reproducer for this is:
> $ guestfish -N test.img=fs:ext4:2G resize2fs-size /dev/sda1 1073741824
> 
> As result, try to mount the filesystem, and get its actual statistics to
> determine its full size. In case mounting fails, fall back to the
> previous method, which is still a good value in the majority of the
> cases.
> 
> Thanks to: Erik Skultety.
> ---
>  cat/filesystems.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/cat/filesystems.c b/cat/filesystems.c
> index cec3c4e47..2b95d3112 100644
> --- a/cat/filesystems.c
> +++ b/cat/filesystems.c
> @@ -508,7 +508,23 @@ do_output_filesystems (void)
>        guestfs_pop_error_handler (g);
>  
>        if (!device || !subvolume) {
> -        size = guestfs_blockdev_getsize64 (g, fses[i]);
> +        /* Try mounting and stating the device.  This might reasonably
> +         * fail, so don't show errors.
> +         */
> +        guestfs_push_error_handler (g, NULL, NULL);
> +
> +        if (guestfs_mount_ro (g, fses[i], "/") == 0) {
> +          CLEANUP_FREE_STATVFS struct guestfs_statvfs *stat = NULL;
> +
> +          stat = guestfs_statvfs (g, "/");
> +          size = stat->blocks * stat->bsize;
> +          guestfs_umount_all (g);
> +        } else {
> +          size = guestfs_blockdev_getsize64 (g, fses[i]);
> +        }
> +
> +        guestfs_pop_error_handler (g);
> +
>          if (size == -1)
>            exit (EXIT_FAILURE);
>        }

Yes this is sensible, ACK.

Thanks,

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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