Re: [Virtio-fs] [PATCH] virtiofsd: Do not support blocking flock

[Greg Kurz]

On Tue, 11 Jan 2022 19:10:43 +0100
Sebastian Hasler  wrote:

> With the current implementation, blocking flock can lead to
> deadlock. Thus, it's better to return EOPNOTSUPP if a user attempts
> to perform a blocking flock request.
> 
> Signed-off-by: Sebastian Hasler 
> ---
>  tools/virtiofsd/passthrough_ll.c | 6 ++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/tools/virtiofsd/passthrough_ll.c 
> b/tools/virtiofsd/passthrough_ll.c
> index 64b5b4fbb1..f3cc307f6d 100644
> --- a/tools/virtiofsd/passthrough_ll.c
> +++ b/tools/virtiofsd/passthrough_ll.c
> @@ -2442,6 +2442,12 @@ static void lo_flock(fuse_req_t req, fuse_ino_t ino, 
> struct fuse_file_info *fi,
>  int res;
>  (void)ino;
>  
> +if (!(op & LOCK_NB)) {
> +/* Blocking flock is not supported */

This paraphrases the code. It would be more informative to provide
an explanation, something like /* Blocking flock can deadlock */ .

No big deal.

Reviewed-by: Greg Kurz 

> +fuse_reply_err(req, EOPNOTSUPP);
> +return;
> +}
> +
>  res = flock(lo_fi_fd(req, fi), op);
>  
>  fuse_reply_err(req, res == -1 ? errno : 0);

Re: [PATCH] virtiofsd: Do not support blocking flock

[Sebastian Hasler]

On 11/01/2022 19:10, Sebastian Hasler wrote:

With the current implementation, blocking flock can lead to
deadlock. Thus, it's better to return EOPNOTSUPP if a user attempts
to perform a blocking flock request.

Signed-off-by: Sebastian Hasler 
---
  tools/virtiofsd/passthrough_ll.c | 6 ++
  1 file changed, 6 insertions(+)

diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
index 64b5b4fbb1..f3cc307f6d 100644
--- a/tools/virtiofsd/passthrough_ll.c
+++ b/tools/virtiofsd/passthrough_ll.c
@@ -2442,6 +2442,12 @@ static void lo_flock(fuse_req_t req, fuse_ino_t ino, 
struct fuse_file_info *fi,
  int res;
  (void)ino;
  
+if (!(op & LOCK_NB)) {

+/* Blocking flock is not supported */
+fuse_reply_err(req, EOPNOTSUPP);
+return;
+}
+
  res = flock(lo_fi_fd(req, fi), op);
  
  fuse_reply_err(req, res == -1 ? errno : 0);


I tested this patch by cherry-picking it on v6.1.0 and using it with 
Kata Containers 2.3.0. The bash code


    exec 42>/lock/flock
    flock -w 120 42

outputs

    flock: 42: Operation not supported

while the bash code

    exec 42>/lock/flock
    flock --nonblock 42

still works. So it works as intended.

--
Sebastian Hasler

stuvus – Studierendenvertretung Universität Stuttgart

[PATCH] virtiofsd: Do not support blocking flock

[Sebastian Hasler]

With the current implementation, blocking flock can lead to
deadlock. Thus, it's better to return EOPNOTSUPP if a user attempts
to perform a blocking flock request.

Signed-off-by: Sebastian Hasler 
---
 tools/virtiofsd/passthrough_ll.c | 6 ++
 1 file changed, 6 insertions(+)

diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
index 64b5b4fbb1..f3cc307f6d 100644
--- a/tools/virtiofsd/passthrough_ll.c
+++ b/tools/virtiofsd/passthrough_ll.c
@@ -2442,6 +2442,12 @@ static void lo_flock(fuse_req_t req, fuse_ino_t ino, 
struct fuse_file_info *fi,
 int res;
 (void)ino;
 
+if (!(op & LOCK_NB)) {
+/* Blocking flock is not supported */
+fuse_reply_err(req, EOPNOTSUPP);
+return;
+}
+
 res = flock(lo_fi_fd(req, fi), op);
 
 fuse_reply_err(req, res == -1 ? errno : 0);
-- 
2.33.1