On 08/18/2015 05:10 PM, Max Reitz wrote: > Split the part which actually refreshes the BlockDriverState.filename > field off of bdrv_refresh_filename() into a more generic function > bdrv_filename(), which first calls bdrv_refresh_filename() and then > stores a qemu-usable filename into the given buffer instead of > BlockDriverState.filename. > > Since bdrv_refresh_filename() therefore no longer refreshes that field, > some calls to that function have to be replaced by calls to > bdrv_filename() "manually" refreshing the BDS filename field (this is > only temporary). > > Additionally, a wrapper function bdrv_filename_alloc() is added which > allocates a buffer of size PATH_MAX, call bdrv_filename() on that buffer > and returns it, since needing a temporary buffer for the filename is a > rather common pattern. > > Signed-off-by: Max Reitz <mre...@redhat.com> > --- > block.c | 39 ++++++++++++++++++++++++++++++++------- > block/blkverify.c | 3 ++- > block/quorum.c | 2 +- > include/block/block.h | 2 ++ > 4 files changed, 37 insertions(+), 9 deletions(-) >
> +/* First refreshes exact_filename and full_open_options by calling
> + * bdrv_refresh_filename(). Then, if exact_filename is set, it is copied into
> + * the target buffer. Otherwise, full_open_options is converted to a JSON
> + * object, prefixed with "json:" (for use through the JSON pseudo protocol)
> and
> + * put there.
> + *
> + * If sz > 0, the string put into the buffer will always be null-terminated.
> + *
> + * Returns @dest.
> + */
> +char *bdrv_filename(BlockDriverState *bs, char *dest, size_t sz)
> +{
How does one tell if 'sz' was large enough, vs. too short and therefore
the snprintf() truncated the resulting string? Would the code be any
simpler if this always returned a freshly g_malloc'd string of the right
length, rather than making the caller have to pre-allocate and guess
whether the allocation was big enough?
> + bdrv_refresh_filename(bs);
> +
> + if (sz > INT_MAX) {
> + sz = INT_MAX;
> + }
>
> if (bs->exact_filename[0]) {
> - pstrcpy(bs->filename, sizeof(bs->filename), bs->exact_filename);
> + pstrcpy(dest, sz, bs->exact_filename);
> } else if (bs->full_open_options) {
> QString *json = qobject_to_json(QOBJECT(bs->full_open_options));
> - snprintf(bs->filename, sizeof(bs->filename), "json:%s",
> - qstring_get_str(json));
> + snprintf(dest, sz, "json:%s", qstring_get_str(json));
> QDECREF(json);
> }
> +
> + return dest;
In other words, I think it's very dangerous to use snprintf() without
checking whether the result fit.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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