[libvirt] [PATCHv4 8/8] storage: probe qcow2 volumes in gluster pool

[Daniel P. Berrange]

On Fri, Nov 22, 2013 at 08:20:30PM -0700, Eric Blake wrote:
> Putting together pieces from previous patches, it is now possible
> for 'virsh vol-dumpxml --pool gluster volname' to report metadata
> about a qcow2 file stored on gluster.  The backing file is still
> treated as raw; to fix that, more patches are needed to make the
> storage backing chain analysis recursive rather than halting at
> a network protocol name, but that work will not need any further
> calls into libgfapi so much as just reusing this code, and that
> should be the only code outside of the storage driver that needs
> any help from libgfapi.  Any additional use of libgfapi within
> libvirt should only be needed for implementing storage pool APIs
> such as volume creation or resizing, where backing chain analysis
> should be unaffected.
> 
> * src/storage/storage_backend_gluster.c
> (virStorageBackendGlusterReadHeader): New helper function.
> (virStorageBackendGlusterRefreshVol): Probe non-raw files.
> 
> Signed-off-by: Eric Blake <eblake at redhat.com>
> ---
>  src/storage/storage_backend_gluster.c | 76 ++++++++++++++++++++++++++++++++++-
>  1 file changed, 75 insertions(+), 1 deletion(-)
> 
> diff --git a/src/storage/storage_backend_gluster.c b/src/storage/storage_backend_gluster.c
> index e935583..b239880 100644
> --- a/src/storage/storage_backend_gluster.c
> +++ b/src/storage/storage_backend_gluster.c
> @@ -147,6 +147,37 @@ error:
>  }
> 
> 
> +static ssize_t
> +virStorageBackendGlusterReadHeader(glfs_fd_t *fd,
> +                                   const char *name,
> +                                   ssize_t maxlen,
> +                                   char **buf)
> +{
> +    char *s;
> +    size_t nread = 0;
> +
> +    if (VIR_ALLOC_N(*buf, maxlen) < 0)
> +        return -1;
> +
> +    s = *buf;
> +    while (maxlen) {
> +        ssize_t r = glfs_read(fd, s, maxlen, 0);
> +        if (r < 0 && errno == EINTR)
> +            continue;
> +        if (r < 0) {
> +            VIR_FREE(*buf);
> +            virReportSystemError(errno, _("unable to read '%s'"), name);
> +            return r;
> +        }

Further down you're requesting O_NONBLOCK, and here you are
not handling EAGAIN explicitly. Is is desirable that we turn
EAGAIN into a fatal error, or should we remove the O_NONBLOCK
flag ?


> @@ -208,15 +243,54 @@ virStorageBackendGlusterRefreshVol(virStorageBackendGlusterStatePtr state,
>          goto cleanup;
>      }
> 
> -    /* FIXME - must open files to determine if they are non-raw */
>      vol->type = VIR_STORAGE_VOL_NETWORK;
>      vol->target.format = VIR_STORAGE_FILE_RAW;
> +    if (!(fd = glfs_open(state->vol, name, O_RDONLY| O_NONBLOCK | O_NOCTTY))) {
> +        /* A dangling symlink now implies a TOCTTOU race; report it.  */
> +        virReportSystemError(errno, _("cannot open volume '%s'"), name);
> +        goto cleanup;
> +    }

Daniel
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