Re: [PATCH] fuse: Return EPERM rather than ENOSYS from link()

[Miklos Szeredi <miklos@szeredi.hu>]

On Fri, 14 Feb 2025 at 02:18, Matt Johnston <matt@codeconstruct.com.au> wrote:
>
> link() is documented to return EPERM when a filesystem doesn't support
> the operation, return that instead.

Applied, thanks.

Also added the following optimization patch if link is not supported.

Thanks,
Miklos

From 150b838b03e887f4e5ffdadcffafef698e34c619 Mon Sep 17 00:00:00 2001
From: Miklos Szeredi <mszeredi@redhat.com>
Date: Fri, 14 Feb 2025 11:00:53 +0100
Subject: [PATCH] fuse: optmize missing FUSE_LINK support

If filesystem doesn't support FUSE_LINK (i.e. returns -ENOSYS), then
remember this and next time return immediately, without incurring the
overhead of a round trip to the server.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/fuse/dir.c    | 9 ++++++++-
 fs/fuse/fuse_i.h | 3 +++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index f07ccaefd1ec..589e88822368 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1123,6 +1123,9 @@ static int fuse_link(struct dentry *entry,
struct inode *newdir,
        struct fuse_mount *fm = get_fuse_mount(inode);
        FUSE_ARGS(args);

+       if (fm->fc->no_link)
+               goto out;
+
        memset(&inarg, 0, sizeof(inarg));
        inarg.oldnodeid = get_node_id(inode);
        args.opcode = FUSE_LINK;
@@ -1138,7 +1141,11 @@ static int fuse_link(struct dentry *entry,
struct inode *newdir,
                fuse_invalidate_attr(inode);

        if (err == -ENOSYS)
-               err = -EPERM;
+               fm->fc->no_link = 1;
+out:
+       if (fm->fc->no_link)
+               return -EPERM;
+
        return err;
 }

diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index fee96fe7887b..3ad5d4b8f7c5 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -867,6 +867,9 @@ struct fuse_conn {
        /* Use pages instead of pointer for kernel I/O */
        unsigned int use_pages_for_kvec_io:1;

+       /* Is link not implemented by fs? */
+       unsigned int no_link:1;
+
        /* Use io_uring for communication */
        unsigned int io_uring;

-- 
2.48.1