Re: [PATCH v3 03/10] virtiofsd: Use lo_inode_open() instead of openat()

[Vivek Goyal]

On Fri, Jul 30, 2021 at 05:01:27PM +0200, Max Reitz wrote:
> The xattr functions want a non-O_PATH FD, so they reopen the lo_inode.fd
> with the flags they need through /proc/self/fd.
> 
> Similarly, lo_opendir() needs an O_RDONLY FD.  Instead of the
> /proc/self/fd trick, it just uses openat(fd, "."), because the FD is
> guaranteed to be a directory, so this works.

Ok, given now lo_opendir() will use lo_inode_open(), it will switch
to using proc O_PATH fd trick. I guess that should be fine.

Vivek

> 
> All cases have one problem in common, though: In the future, when we may
> have a file handle in the lo_inode instead of an FD, querying an
> lo_inode FD may incur an open_by_handle_at() call.  It does not make
> sense to then reopen that FD with custom flags, those should have been
> passed to open_by_handle_at() instead.
> 
> Use lo_inode_open() instead of openat().  As part of the file handle
> change, lo_inode_open() will be made to invoke openat() only if
> lo_inode.fd is valid.  Otherwise, it will invoke open_by_handle_at()
> with the right flags from the start.
> 
> Consequently, after this patch, lo_inode_open() is the only place to
> invoke openat() to reopen an existing FD with different flags.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  tools/virtiofsd/passthrough_ll.c | 43 ++++++++++++++++++++------------
>  1 file changed, 27 insertions(+), 16 deletions(-)
> 
> diff --git a/tools/virtiofsd/passthrough_ll.c 
> b/tools/virtiofsd/passthrough_ll.c
> index fb5e073e6a..a444c3a7e2 100644
> --- a/tools/virtiofsd/passthrough_ll.c
> +++ b/tools/virtiofsd/passthrough_ll.c
> @@ -1729,18 +1729,26 @@ static void lo_opendir(fuse_req_t req, fuse_ino_t ino,
>  {
>      int error = ENOMEM;
>      struct lo_data *lo = lo_data(req);
> -    struct lo_dirp *d;
> +    struct lo_inode *inode;
> +    struct lo_dirp *d = NULL;
>      int fd;
>      ssize_t fh;
>  
> +    inode = lo_inode(req, ino);
> +    if (!inode) {
> +        error = EBADF;
> +        goto out_err;
> +    }
> +
>      d = calloc(1, sizeof(struct lo_dirp));
>      if (d == NULL) {
>          goto out_err;
>      }
>  
> -    fd = openat(lo_fd(req, ino), ".", O_RDONLY);
> -    if (fd == -1) {
> -        goto out_errno;
> +    fd = lo_inode_open(lo, inode, O_RDONLY);
> +    if (fd < 0) {
> +        error = -fd;
> +        goto out_err;
>      }
>  
>      d->dp = fdopendir(fd);
> @@ -1769,6 +1777,7 @@ static void lo_opendir(fuse_req_t req, fuse_ino_t ino,
>  out_errno:
>      error = errno;
>  out_err:
> +    lo_inode_put(lo, &inode);
>      if (d) {
>          if (d->dp) {
>              closedir(d->dp);
> @@ -2973,7 +2982,6 @@ static void lo_getxattr(fuse_req_t req, fuse_ino_t ino, 
> const char *in_name,
>          }
>      }
>  
> -    sprintf(procname, "%i", inode->fd);
>      /*
>       * It is not safe to open() non-regular/non-dir files in file server
>       * unless O_PATH is used, so use that method for regular files/dir
> @@ -2981,13 +2989,15 @@ static void lo_getxattr(fuse_req_t req, fuse_ino_t 
> ino, const char *in_name,
>       * Otherwise, call fchdir() to avoid open().
>       */
>      if (S_ISREG(inode->filetype) || S_ISDIR(inode->filetype)) {
> -        fd = openat(lo->proc_self_fd, procname, O_RDONLY);
> +        fd = lo_inode_open(lo, inode, O_RDONLY);
>          if (fd < 0) {
> -            goto out_err;
> +            saverr = -fd;
> +            goto out;
>          }
>          ret = fgetxattr(fd, name, value, size);
>          saverr = ret == -1 ? errno : 0;
>      } else {
> +        sprintf(procname, "%i", inode->fd);
>          /* fchdir should not fail here */
>          FCHDIR_NOFAIL(lo->proc_self_fd);
>          ret = getxattr(procname, name, value, size);
> @@ -3054,15 +3064,16 @@ static void lo_listxattr(fuse_req_t req, fuse_ino_t 
> ino, size_t size)
>          }
>      }
>  
> -    sprintf(procname, "%i", inode->fd);
>      if (S_ISREG(inode->filetype) || S_ISDIR(inode->filetype)) {
> -        fd = openat(lo->proc_self_fd, procname, O_RDONLY);
> +        fd = lo_inode_open(lo, inode, O_RDONLY);
>          if (fd < 0) {
> -            goto out_err;
> +            saverr = -fd;
> +            goto out;
>          }
>          ret = flistxattr(fd, value, size);
>          saverr = ret == -1 ? errno : 0;
>      } else {
> +        sprintf(procname, "%i", inode->fd);
>          /* fchdir should not fail here */
>          FCHDIR_NOFAIL(lo->proc_self_fd);
>          ret = listxattr(procname, value, size);
> @@ -3211,14 +3222,14 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t 
> ino, const char *in_name,
>       * setxattr() on the link's filename there.
>       */
>      open_inode = S_ISREG(inode->filetype) || S_ISDIR(inode->filetype);
> -    sprintf(procname, "%i", inode->fd);
>      if (open_inode) {
> -        fd = openat(lo->proc_self_fd, procname, O_RDONLY);
> +        fd = lo_inode_open(lo, inode, O_RDONLY);
>          if (fd < 0) {
> -            saverr = errno;
> +            saverr = -fd;
>              goto out;
>          }
>      } else {
> +        sprintf(procname, "%i", inode->fd);
>          /* fchdir should not fail here */
>          FCHDIR_NOFAIL(lo->proc_self_fd);
>      }
> @@ -3317,16 +3328,16 @@ static void lo_removexattr(fuse_req_t req, fuse_ino_t 
> ino, const char *in_name)
>      fuse_log(FUSE_LOG_DEBUG, "lo_removexattr(ino=%" PRIu64 ", name=%s)\n", 
> ino,
>               name);
>  
> -    sprintf(procname, "%i", inode->fd);
>      if (S_ISREG(inode->filetype) || S_ISDIR(inode->filetype)) {
> -        fd = openat(lo->proc_self_fd, procname, O_RDONLY);
> +        fd = lo_inode_open(lo, inode, O_RDONLY);
>          if (fd < 0) {
> -            saverr = errno;
> +            saverr = -fd;
>              goto out;
>          }
>          ret = fremovexattr(fd, name);
>          saverr = ret == -1 ? errno : 0;
>      } else {
> +        sprintf(procname, "%i", inode->fd);
>          /* fchdir should not fail here */
>          FCHDIR_NOFAIL(lo->proc_self_fd);
>          ret = removexattr(procname, name);
> -- 
> 2.31.1
>