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[82.29.237.198]) by smtp.gmail.com with ESMTPSA id w8sm7800507wrt.83.2021.06.30.03.17.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 30 Jun 2021 03:17:16 -0700 (PDT) Date: Wed, 30 Jun 2021 11:17:15 +0100 From: "Dr. David Alan Gilbert" To: Greg Kurz Subject: Re: [Virtio-fs] [PATCH v7 1/7] virtiofsd: Fix fuse setxattr() API change issue Message-ID: References: <20210622150852.1507204-1-vgoyal@redhat.com> <20210622150852.1507204-2-vgoyal@redhat.com> <20210629144431.02e2ce0c@bahia.lan> MIME-Version: 1.0 In-Reply-To: <20210629144431.02e2ce0c@bahia.lan> User-Agent: Mutt/2.0.7 (2021-05-04) Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.133.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.435, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=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: virtio-fs@redhat.com, qemu-devel@nongnu.org, Vivek Goyal , miklos@szeredi.hu Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Greg Kurz (groug@kaod.org) wrote: > On Mon, 28 Jun 2021 15:46:40 +0100 > "Dr. David Alan Gilbert" wrote: > > > * Vivek Goyal (vgoyal@redhat.com) wrote: > > > With kernel header updates fuse_setxattr_in struct has grown in size. > > > But this new struct size only takes affect if user has opted in > > > for fuse feature FUSE_SETXATTR_EXT otherwise fuse continues to > > > send "fuse_setxattr_in" of older size. Older size is determined > > > by FUSE_COMPAT_SETXATTR_IN_SIZE. > > > > > > Fix this. If we have not opted in for FUSE_SETXATTR_EXT, then > > > expect that we will get fuse_setxattr_in of size FUSE_COMPAT_SETXATTR_IN_SIZE > > > and not sizeof(struct fuse_sexattr_in). > > > > > > Signed-off-by: Vivek Goyal > > > > Yeh it's a bit of a grim fix, but I think it's the best we can do, and > > we need to get it in since the headers have already been merged. > > You can also add: > > Fixes: 278f064e4524 ("Update Linux headers to 5.13-rc4") > > because this is basically what happened : this commit exposes the API > breakage. > > This is kinda problematic : linux kernel headers are updated globally, > i.e. an header update merged by some other subsystem will unknowingly > break virtiofsd each time we face a similar situation. > > We could cope with it if the code was adapted to API changes when > needed, e.g. this patch squashed into 278f064e4524 . It doesn't > seem that can be achievable without some automation to detect > buggy situations (e.g. code depends on the size of a structure). > And even with that, it would still cause the subsystem that > needs the header update to depend on other subsystems to > fix the breakage. > > Another possibility could maybe to stop doing global updates and > let each subsystem handle the kernel headers it needs. > > OR we could avoid breaking the API in the kernel in the first > place. That would be my preference! Dave > Thoughts ? > > Anyway, the fix is good: > > Reviewed-by: Greg Kurz > > > (I don't think libfuse has a fix for this in yet itself, but it might > > survive because it doesn't bother copying the data like we do with > > mbuf). > > > > > > Reviewed-by: Dr. David Alan Gilbert > > > > > --- > > > tools/virtiofsd/fuse_common.h | 5 +++++ > > > tools/virtiofsd/fuse_lowlevel.c | 7 ++++++- > > > 2 files changed, 11 insertions(+), 1 deletion(-) > > > > > > diff --git a/tools/virtiofsd/fuse_common.h b/tools/virtiofsd/fuse_common.h > > > index fa9671872e..0c2665b977 100644 > > > --- a/tools/virtiofsd/fuse_common.h > > > +++ b/tools/virtiofsd/fuse_common.h > > > @@ -372,6 +372,11 @@ struct fuse_file_info { > > > */ > > > #define FUSE_CAP_HANDLE_KILLPRIV_V2 (1 << 28) > > > > > > +/** > > > + * Indicates that file server supports extended struct fuse_setxattr_in > > > + */ > > > +#define FUSE_CAP_SETXATTR_EXT (1 << 29) > > > + > > > /** > > > * Ioctl flags > > > * > > > diff --git a/tools/virtiofsd/fuse_lowlevel.c b/tools/virtiofsd/fuse_lowlevel.c > > > index 7fe2cef1eb..c2b6ff1686 100644 > > > --- a/tools/virtiofsd/fuse_lowlevel.c > > > +++ b/tools/virtiofsd/fuse_lowlevel.c > > > @@ -1419,8 +1419,13 @@ static void do_setxattr(fuse_req_t req, fuse_ino_t nodeid, > > > struct fuse_setxattr_in *arg; > > > const char *name; > > > const char *value; > > > + bool setxattr_ext = req->se->conn.want & FUSE_CAP_SETXATTR_EXT; > > > > > > - arg = fuse_mbuf_iter_advance(iter, sizeof(*arg)); > > > + if (setxattr_ext) { > > > + arg = fuse_mbuf_iter_advance(iter, sizeof(*arg)); > > > + } else { > > > + arg = fuse_mbuf_iter_advance(iter, FUSE_COMPAT_SETXATTR_IN_SIZE); > > > + } > > > name = fuse_mbuf_iter_advance_str(iter); > > > if (!arg || !name) { > > > fuse_reply_err(req, EINVAL); > > > -- > > > 2.25.4 > > > > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK