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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <5d5f930424c1c770754041aa8ad6421dc4e2b58e.1596536719.git.lukasstraub2@web.de> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mreitz@redhat.com X-Mimecast-Spam-Score: 0.002 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: 8bit Content-Language: en-US Received-SPF: pass client-ip=216.205.24.124; envelope-from=mreitz@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/02 01:13:52 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -23 X-Spam_score: -2.4 X-Spam_bar: -- X-Spam_report: (-2.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.324, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Alberto Garcia , "Dr. David Alan Gilbert" , Wainer dos Santos Moschetta , Zhang Chen , Cleber Rosa , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 04.08.20 12:46, Lukas Straub wrote: > If we remove the child with the highest index from the quorum, > decrement s->next_child_index. This way we get stable children > names as long as we only remove the last child. > > Signed-off-by: Lukas Straub > Fixes: https://bugs.launchpad.net/bugs/1881231 > Reviewed-by: Zhang Chen > Reviewed-by: Alberto Garcia > --- > block/quorum.c | 20 ++++++++++++++------ > 1 file changed, 14 insertions(+), 6 deletions(-) > > diff --git a/block/quorum.c b/block/quorum.c > index 6df9449fc2..e846a7e892 100644 > --- a/block/quorum.c > +++ b/block/quorum.c > @@ -29,6 +29,8 @@ > > #define HASH_LENGTH 32 > > +#define INDEXSTR_LEN 32 > + I don’t like this too much. There is no real concept such as an index string, and it doesn’t have a fixed length. It just so happens that there are a couple of places where we need some buffer to snprintf() into, and all those places happen to use 32 because that’s definitely sufficient for “children.%u”. (Technically, it should not be fixed to 32, but “sizeof("children.") + ceil(log_10(INT_MAX))”.) Whenever we then use such a buffer, we shouldn’t use the same hard-coded magic number or constant, but instead just refer to the size of the buffer: > #define QUORUM_OPT_VOTE_THRESHOLD "vote-threshold" > #define QUORUM_OPT_BLKVERIFY "blkverify" > #define QUORUM_OPT_REWRITE "rewrite-corrupted" > @@ -970,9 +972,9 @@ static int quorum_open(BlockDriverState *bs, QDict *options, int flags, > opened = g_new0(bool, s->num_children); > > for (i = 0; i < s->num_children; i++) { > - char indexstr[32]; > - ret = snprintf(indexstr, 32, "children.%d", i); > - assert(ret < 32); > + char indexstr[INDEXSTR_LEN]; > + ret = snprintf(indexstr, INDEXSTR_LEN, "children.%d", i); > + assert(ret < INDEXSTR_LEN); So in lines 2 and 3 here we should just use sizeof(indexstr). > > s->children[i] = bdrv_open_child(NULL, options, indexstr, bs, > &child_of_bds, BDRV_CHILD_DATA, false, > @@ -1024,7 +1026,7 @@ static void quorum_add_child(BlockDriverState *bs, BlockDriverState *child_bs, > { > BDRVQuorumState *s = bs->opaque; > BdrvChild *child; > - char indexstr[32]; > + char indexstr[INDEXSTR_LEN]; > int ret; > > if (s->is_blkverify) { > @@ -1039,8 +1041,8 @@ static void quorum_add_child(BlockDriverState *bs, BlockDriverState *child_bs, > return; > } > > - ret = snprintf(indexstr, 32, "children.%u", s->next_child_index); > - if (ret < 0 || ret >= 32) { > + ret = snprintf(indexstr, INDEXSTR_LEN, "children.%u", s->next_child_index); > + if (ret < 0 || ret >= INDEXSTR_LEN) { Same here. > error_setg(errp, "cannot generate child name"); > return; > } > @@ -1068,6 +1070,7 @@ static void quorum_del_child(BlockDriverState *bs, BdrvChild *child, > Error **errp) > { > BDRVQuorumState *s = bs->opaque; > + char indexstr[INDEXSTR_LEN]; > int i; > > for (i = 0; i < s->num_children; i++) { > @@ -1089,6 +1092,11 @@ static void quorum_del_child(BlockDriverState *bs, BdrvChild *child, > /* We know now that num_children > threshold, so blkverify must be false */ > assert(!s->is_blkverify); > > + snprintf(indexstr, INDEXSTR_LEN, "children.%u", s->next_child_index - 1); > + if (!strncmp(child->name, indexstr, INDEXSTR_LEN)) { And here. I also wonder if there should be an assertion/check checking snprintf’s return value (as is done in the other places), but then again, it doesn’t really matter. But it would make the length limitation of strncmp() superfluous and a plain strcmp() would suffice. (I don’t like strncmp() very much here, because we have a problem if indexstr’s length doesn’t suffice to hold children.%u, and we then compare only the first INDEXSTR_LEN bytes with child->name. That would be a bug. Just a different bug than an out-of-bounds read.) > + s->next_child_index--; > + } > + > bdrv_drained_begin(bs); > > /* We can safely remove this child now */ Now, all in all, it doesn’t really matter of course. This patch works and introducing INDEXSTR_LEN isn’t worse than just using 32 as a magic number. So I’ll take the patch as-is for now – if you think that using sizeof(indexstr) and/or replacing the strncmp() by assert()+strcmp() would be so much better to justify a v4 (of this patch) or a follow-up patch, then, well, that could still be done. O:) tl;dr: Thanks, I’ve applied this patch to my block branch: https://git.xanclic.moe/XanClic/qemu/commits/branch/block Max