Re: [PATCH v3 04/10] virtiofsd: Add lo_inode_fd() helper

[Max Reitz]

On 06.08.21 20:25, Vivek Goyal wrote:
> On Fri, Jul 30, 2021 at 05:01:28PM +0200, Max Reitz wrote:
>
> [..]
> > @@ -1335,12 +1359,18 @@ static void lo_mknod_symlink(fuse_req_t req, fuse_ino_t 
> > parent,
> >           return;
> >       }
> >   
> > +    res = lo_inode_fd(dir, &dir_fd);
> > +    if (res < 0) {
> > +        saverr = -res;
> > +        goto out;
> > +    }
> > +
> >       saverr = lo_change_cred(req, &old, lo->change_umask && !S_ISLNK(mode));
> >       if (saverr) {
> >           goto out;
> >       }
> >   
> > -    res = mknod_wrapper(dir->fd, name, link, mode, rdev);
> > +    res = mknod_wrapper(dir_fd.fd, name, link, mode, rdev);
> >   
> >       saverr = errno;
> >   
> > @@ -1388,6 +1418,8 @@ static void lo_symlink(fuse_req_t req, const char *link, fuse_ino_t parent,
> >   static void lo_link(fuse_req_t req, fuse_ino_t ino, fuse_ino_t parent,
> >                       const char *name)
> >   {
> > +    g_auto(TempFd) inode_fd = TEMP_FD_INIT;
> > +    g_auto(TempFd) parent_fd = TEMP_FD_INIT;
> >       int res;
> >       struct lo_data *lo = lo_data(req);
> >       struct lo_inode *parent_inode;
> > @@ -1413,18 +1445,31 @@ static void lo_link(fuse_req_t req, fuse_ino_t ino, 
> > fuse_ino_t parent,
> >           goto out_err;
> >       }
> >   
> > +    res = lo_inode_fd(inode, &inode_fd);
> > +    if (res < 0) {
> > +        errno = -res;
> In previous function, we saved error to "saverr" and jumped to "out"
> label, instead of overwriting to errno.
>
> I would think that it will be good to use a single pattern. Either
> save error in saverr or overwrite errno. I personally prefer saving
> error into "saverr".

Absolutely, will do.

> > +        goto out_err;
> > +    }
> > +
> > +    res = lo_inode_fd(parent_inode, &parent_fd);
> > +    if (res < 0) {
> > +        errno = -res;
> > +        goto out_err;
> > +    }
> > +
> >       memset(&e, 0, sizeof(struct fuse_entry_param));
> >       e.attr_timeout = lo->timeout;
> >       e.entry_timeout = lo->timeout;
> >   
> > -    sprintf(procname, "%i", inode->fd);
> > -    res = linkat(lo->proc_self_fd, procname, parent_inode->fd, name,
> > +    sprintf(procname, "%i", inode_fd.fd);
> > +    res = linkat(lo->proc_self_fd, procname, parent_fd.fd, name,
> >                    AT_SYMLINK_FOLLOW);
> >       if (res == -1) {
> >           goto out_err;
> >       }
> >   
> > -    res = fstatat(inode->fd, "", &e.attr, AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW);
> > +    res = fstatat(inode_fd.fd, "", &e.attr,
> > +                  AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW);
> >       if (res == -1) {
> >           goto out_err;
> >       }
> > @@ -1453,23 +1498,33 @@ out_err:
> >   static struct lo_inode *lookup_name(fuse_req_t req, fuse_ino_t parent,
> >                                       const char *name)
> >   {
> > +    g_auto(TempFd) dir_fd = TEMP_FD_INIT;
> >       int res;
> >       uint64_t mnt_id;
> >       struct stat attr;
> >       struct lo_data *lo = lo_data(req);
> >       struct lo_inode *dir = lo_inode(req, parent);
> > +    struct lo_inode *inode = NULL;
> >   
> >       if (!dir) {
> > -        return NULL;
> > +        goto out;
> Should we continue to just call "return NULL". dir is NULL. That means
> lo_inode() failed. That means we never got the reference. So we don't
> have to put the reference. If we do "goto out", it will call
> lo_inode_put() which is not needed.

Yes, but lo_inode_put() will handle this gracefully, so it isn’t wrong. 
My personal preference is that if there is an clean-up path, it should 
be used everywhere instead of having pure returns at the beginning of a 
function (where not many resources have been initialized yet), so that 
no clean-up will be forgotten.  Like, if we were to add some resource 
acquisition in the declarations above (and clean-up code in the clean-up 
path), we would need to change the return to a goto here.  Or maybe we’d 
forget that, and then we’d leak something.

So I prefer having clean-up sections be generic enough that they can be 
used from anywhere within the function, and then also use it from 
anywhere within the function, even if they end up being no-ops.

> >       }
> >   
> > -    res = do_statx(lo, dir->fd, name, &attr, AT_SYMLINK_NOFOLLOW, &mnt_id);
> > -    lo_inode_put(lo, &dir);
> > +    res = lo_inode_fd(dir, &dir_fd);
> > +    if (res < 0) {
> > +        goto out;
> > +    }
> > +
> > +    res = do_statx(lo, dir_fd.fd, name, &attr, AT_SYMLINK_NOFOLLOW, &mnt_id);
> >       if (res == -1) {
> > -        return NULL;
> > +        goto out;
> >       }
> >   
> > -    return lo_find(lo, &attr, mnt_id);
> > +    inode = lo_find(lo, &attr, mnt_id);
> > +
> > +out:
> > +    lo_inode_put(lo, &dir);
> > +    return inode;
> >   }
>
> Thanks
> Vivek