Re: [PATCH v5 3/9] virtiofsd: Parse extended "struct fuse_init_in"

[Vivek Goyal]

On Thu, Feb 03, 2022 at 06:56:58PM +0000, Dr. David Alan Gilbert wrote:
> * Vivek Goyal (vgoyal@redhat.com) wrote:
> > Add some code to parse extended "struct fuse_init_in". And use a local
> > variable "flag" to represent 64 bit flags. This will make it easier
> > to add more features without having to worry about two 32bit flags (->flags
> > and ->flags2) in "fuse_struct_in".
> > 
> > Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
> > ---
> >  tools/virtiofsd/fuse_lowlevel.c | 62 +++++++++++++++++++++------------
> >  1 file changed, 40 insertions(+), 22 deletions(-)
> > 
> > diff --git a/tools/virtiofsd/fuse_lowlevel.c 
> > b/tools/virtiofsd/fuse_lowlevel.c
> > index ce29a70253..1f10dcc75b 100644
> > --- a/tools/virtiofsd/fuse_lowlevel.c
> > +++ b/tools/virtiofsd/fuse_lowlevel.c
> > @@ -1881,11 +1881,15 @@ static void do_init(fuse_req_t req, fuse_ino_t 
> > nodeid,
> >  {
> >      size_t compat_size = offsetof(struct fuse_init_in, max_readahead);
> >      size_t compat2_size = offsetof(struct fuse_init_in, flags) + 
> > sizeof(uint32_t);
> > +    /* Fuse structure extended with minor version 36 */
> > +    size_t compat3_size = offsetof(struct fuse_init_in, unused) +
> > +                          (11 * sizeof(uint32_t));
> 
> Hmm that's actually quite difficult; what we have at the moment is:
> 
> struct fuse_init_in {
>         uint32_t        major;
>         uint32_t        minor;
>         uint32_t        max_readahead;
>         uint32_t        flags;
>         uint32_t        flags2;
>         uint32_t        unused[11];
> };
> 
> so imagine someone comes along and changes that to:
> 
> struct fuse_init_in {    
>         uint32_t        major;
>         uint32_t        minor;
>         uint32_t        max_readahead;
>         uint32_t        flags;
>         uint32_t        flags2;
>         uint32_t        flags3;
>         uint32_t        unused[10];
> };
> 
> Then this code will break (oddly!), where the old code that didn't reference 
> the
> unusued field wouldn't.

Good catch. I did not think about it.

> It looks like qemu defines an 'endof' macro, so I think you can do:
> 
>   size_t compat3_size = endof(struct fuse_init_in, unused);
> 
> I think that should work as long as people nibble away at unused from
> the top.

Will use "endof" macro.

Thanks
Vivek

> 
> Dave
> 
> 
> >      struct fuse_init_in *arg;
> >      struct fuse_init_out outarg;
> >      struct fuse_session *se = req->se;
> >      size_t bufsize = se->bufsize;
> >      size_t outargsize = sizeof(outarg);
> > +    uint64_t flags = 0;
> >  
> >      (void)nodeid;
> >  
> > @@ -1902,11 +1906,25 @@ static void do_init(fuse_req_t req, fuse_ino_t 
> > nodeid,
> >              fuse_reply_err(req, EINVAL);
> >              return;
> >          }
> > +        flags |= arg->flags;
> > +    }
> > +
> > +    /*
> > +     * fuse_init_in was extended again with minor version 36. Just read
> > +     * current known size of fuse_init so that future extension and
> > +     * header rebase does not cause breakage.
> > +     */
> > +    if (sizeof(*arg) > compat2_size && (arg->flags & FUSE_INIT_EXT)) {
> > +        if (!fuse_mbuf_iter_advance(iter, compat3_size - compat2_size)) {
> > +            fuse_reply_err(req, EINVAL);
> > +            return;
> > +        }
> > +        flags |= (uint64_t) arg->flags2 << 32;
> >      }
> >  
> >      fuse_log(FUSE_LOG_DEBUG, "INIT: %u.%u\n", arg->major, arg->minor);
> >      if (arg->major == 7 && arg->minor >= 6) {
> > -        fuse_log(FUSE_LOG_DEBUG, "flags=0x%08x\n", arg->flags);
> > +        fuse_log(FUSE_LOG_DEBUG, "flags=0x%016llx\n", flags);
> >          fuse_log(FUSE_LOG_DEBUG, "max_readahead=0x%08x\n", 
> > arg->max_readahead);
> >      }
> >      se->conn.proto_major = arg->major;
> > @@ -1934,68 +1952,68 @@ static void do_init(fuse_req_t req, fuse_ino_t 
> > nodeid,
> >      if (arg->max_readahead < se->conn.max_readahead) {
> >          se->conn.max_readahead = arg->max_readahead;
> >      }
> > -    if (arg->flags & FUSE_ASYNC_READ) {
> > +    if (flags & FUSE_ASYNC_READ) {
> >          se->conn.capable |= FUSE_CAP_ASYNC_READ;
> >      }
> > -    if (arg->flags & FUSE_POSIX_LOCKS) {
> > +    if (flags & FUSE_POSIX_LOCKS) {
> >          se->conn.capable |= FUSE_CAP_POSIX_LOCKS;
> >      }
> > -    if (arg->flags & FUSE_ATOMIC_O_TRUNC) {
> > +    if (flags & FUSE_ATOMIC_O_TRUNC) {
> >          se->conn.capable |= FUSE_CAP_ATOMIC_O_TRUNC;
> >      }
> > -    if (arg->flags & FUSE_EXPORT_SUPPORT) {
> > +    if (flags & FUSE_EXPORT_SUPPORT) {
> >          se->conn.capable |= FUSE_CAP_EXPORT_SUPPORT;
> >      }
> > -    if (arg->flags & FUSE_DONT_MASK) {
> > +    if (flags & FUSE_DONT_MASK) {
> >          se->conn.capable |= FUSE_CAP_DONT_MASK;
> >      }
> > -    if (arg->flags & FUSE_FLOCK_LOCKS) {
> > +    if (flags & FUSE_FLOCK_LOCKS) {
> >          se->conn.capable |= FUSE_CAP_FLOCK_LOCKS;
> >      }
> > -    if (arg->flags & FUSE_AUTO_INVAL_DATA) {
> > +    if (flags & FUSE_AUTO_INVAL_DATA) {
> >          se->conn.capable |= FUSE_CAP_AUTO_INVAL_DATA;
> >      }
> > -    if (arg->flags & FUSE_DO_READDIRPLUS) {
> > +    if (flags & FUSE_DO_READDIRPLUS) {
> >          se->conn.capable |= FUSE_CAP_READDIRPLUS;
> >      }
> > -    if (arg->flags & FUSE_READDIRPLUS_AUTO) {
> > +    if (flags & FUSE_READDIRPLUS_AUTO) {
> >          se->conn.capable |= FUSE_CAP_READDIRPLUS_AUTO;
> >      }
> > -    if (arg->flags & FUSE_ASYNC_DIO) {
> > +    if (flags & FUSE_ASYNC_DIO) {
> >          se->conn.capable |= FUSE_CAP_ASYNC_DIO;
> >      }
> > -    if (arg->flags & FUSE_WRITEBACK_CACHE) {
> > +    if (flags & FUSE_WRITEBACK_CACHE) {
> >          se->conn.capable |= FUSE_CAP_WRITEBACK_CACHE;
> >      }
> > -    if (arg->flags & FUSE_NO_OPEN_SUPPORT) {
> > +    if (flags & FUSE_NO_OPEN_SUPPORT) {
> >          se->conn.capable |= FUSE_CAP_NO_OPEN_SUPPORT;
> >      }
> > -    if (arg->flags & FUSE_PARALLEL_DIROPS) {
> > +    if (flags & FUSE_PARALLEL_DIROPS) {
> >          se->conn.capable |= FUSE_CAP_PARALLEL_DIROPS;
> >      }
> > -    if (arg->flags & FUSE_POSIX_ACL) {
> > +    if (flags & FUSE_POSIX_ACL) {
> >          se->conn.capable |= FUSE_CAP_POSIX_ACL;
> >      }
> > -    if (arg->flags & FUSE_HANDLE_KILLPRIV) {
> > +    if (flags & FUSE_HANDLE_KILLPRIV) {
> >          se->conn.capable |= FUSE_CAP_HANDLE_KILLPRIV;
> >      }
> > -    if (arg->flags & FUSE_NO_OPENDIR_SUPPORT) {
> > +    if (flags & FUSE_NO_OPENDIR_SUPPORT) {
> >          se->conn.capable |= FUSE_CAP_NO_OPENDIR_SUPPORT;
> >      }
> > -    if (!(arg->flags & FUSE_MAX_PAGES)) {
> > +    if (!(flags & FUSE_MAX_PAGES)) {
> >          size_t max_bufsize = FUSE_DEFAULT_MAX_PAGES_PER_REQ * 
> > getpagesize() +
> >                               FUSE_BUFFER_HEADER_SIZE;
> >          if (bufsize > max_bufsize) {
> >              bufsize = max_bufsize;
> >          }
> >      }
> > -    if (arg->flags & FUSE_SUBMOUNTS) {
> > +    if (flags & FUSE_SUBMOUNTS) {
> >          se->conn.capable |= FUSE_CAP_SUBMOUNTS;
> >      }
> > -    if (arg->flags & FUSE_HANDLE_KILLPRIV_V2) {
> > +    if (flags & FUSE_HANDLE_KILLPRIV_V2) {
> >          se->conn.capable |= FUSE_CAP_HANDLE_KILLPRIV_V2;
> >      }
> > -    if (arg->flags & FUSE_SETXATTR_EXT) {
> > +    if (flags & FUSE_SETXATTR_EXT) {
> >          se->conn.capable |= FUSE_CAP_SETXATTR_EXT;
> >      }
> >  #ifdef HAVE_SPLICE
> > @@ -2063,7 +2081,7 @@ static void do_init(fuse_req_t req, fuse_ino_t nodeid,
> >      if (se->conn.max_write < bufsize - FUSE_BUFFER_HEADER_SIZE) {
> >          se->bufsize = se->conn.max_write + FUSE_BUFFER_HEADER_SIZE;
> >      }
> > -    if (arg->flags & FUSE_MAX_PAGES) {
> > +    if (flags & FUSE_MAX_PAGES) {
> >          outarg.flags |= FUSE_MAX_PAGES;
> >          outarg.max_pages = (se->conn.max_write - 1) / getpagesize() + 1;
> >      }
> > -- 
> > 2.34.1
> > 
> -- 
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>