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

[Dr. David Alan Gilbert]

* 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.
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.

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