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Message-ID: <CAJnrk1bCenZHzPSrdjxzUMY4ekKhtAJ74Dg1QhUs77A1qEDu3A@mail.gmail.com>
Date: Tue, 6 Jan 2026 17:46:09 -0800
From: Joanne Koong <joannelkoong@...il.com>
To: Horst Birthelmer <hbirthelmer@...glemail.com>
Cc: Miklos Szeredi <miklos@...redi.hu>, Bernd Schubert <bschubert@....com>, linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org, Horst Birthelmer <hbirthelmer@....com>
Subject: Re: [PATCH RFC v2 2/2] fuse: add an implementation of open+getattr
On Tue, Dec 23, 2025 at 2:13 PM Horst Birthelmer
<hbirthelmer@...glemail.com> wrote:
>
> The discussion about compound commands in fuse was
> started over an argument to add a new operation that
> will open a file and return its attributes in the same operation.
>
> Here is a demonstration of that use case with compound commands.
>
> Signed-off-by: Horst Birthelmer <hbirthelmer@....com>
> ---
> fs/fuse/file.c | 125 ++++++++++++++++++++++++++++++++++++++++++++++++-------
> fs/fuse/fuse_i.h | 6 ++-
> fs/fuse/inode.c | 6 +++
> fs/fuse/ioctl.c | 2 +-
> 4 files changed, 121 insertions(+), 18 deletions(-)
>
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index 01bc894e9c2b..507b4c4ba257 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -126,8 +126,84 @@ static void fuse_file_put(struct fuse_file *ff, bool sync)
> }
> }
>
> +static int fuse_compound_open_getattr(struct fuse_mount *fm, u64 nodeid,
> + int flags, int opcode,
> + struct fuse_file *ff,
> + struct fuse_attr_out *outattrp,
> + struct fuse_open_out *outopenp)
> +{
> + struct fuse_compound_req *compound;
> + struct fuse_args open_args = {}, getattr_args = {};
> + struct fuse_open_in open_in = {};
> + struct fuse_getattr_in getattr_in = {};
> + int err;
> +
> + /* Build compound request with flag to execute in the given order */
> + compound = fuse_compound_alloc(fm, 0);
> + if (IS_ERR(compound))
> + return PTR_ERR(compound);
> +
> + /* Add OPEN */
> + open_in.flags = flags & ~(O_CREAT | O_EXCL | O_NOCTTY);
> + if (!fm->fc->atomic_o_trunc)
> + open_in.flags &= ~O_TRUNC;
> +
> + if (fm->fc->handle_killpriv_v2 &&
> + (open_in.flags & O_TRUNC) && !capable(CAP_FSETID)) {
> + open_in.open_flags |= FUSE_OPEN_KILL_SUIDGID;
> + }
> + open_args.opcode = opcode;
> + open_args.nodeid = nodeid;
> + open_args.in_numargs = 1;
> + open_args.in_args[0].size = sizeof(open_in);
> + open_args.in_args[0].value = &open_in;
> + open_args.out_numargs = 1;
> + open_args.out_args[0].size = sizeof(struct fuse_open_out);
> + open_args.out_args[0].value = outopenp;
> +
> + err = fuse_compound_add(compound, &open_args);
> + if (err)
> + goto out;
> +
> + /* Add GETATTR */
> + getattr_args.opcode = FUSE_GETATTR;
> + getattr_args.nodeid = nodeid;
> + getattr_args.in_numargs = 1;
> + getattr_args.in_args[0].size = sizeof(getattr_in);
> + getattr_args.in_args[0].value = &getattr_in;
> + getattr_args.out_numargs = 1;
> + getattr_args.out_args[0].size = sizeof(struct fuse_attr_out);
> + getattr_args.out_args[0].value = outattrp;
I think things end up looking cleaner here (and above for the open
args) if the arg initialization logic gets abstracted into helper
functions, as fuse_do_getattr() and fuse_send_open() have pretty much
the exact same logic.
Thanks,
Joanne
> +
> + err = fuse_compound_add(compound, &getattr_args);
> + if (err)
> + goto out;
> +
> + err = fuse_compound_send(compound);
> + if (err)
> + goto out;
> +
> + /* Check if the OPEN operation succeeded */
> + err = fuse_compound_get_error(compound, 0);
> + if (err)
> + goto out;
> +
> + /* Check if the GETATTR operation succeeded */
> + err = fuse_compound_get_error(compound, 1);
> + if (err)
> + goto out;
> +
> + ff->fh = outopenp->fh;
> + ff->open_flags = outopenp->open_flags;
> +
> +out:
> + fuse_compound_free(compound);
> + return err;
> +}
> +
> struct fuse_file *fuse_file_open(struct fuse_mount *fm, u64 nodeid,
> - unsigned int open_flags, bool isdir)
> + struct inode *inode,
> + unsigned int open_flags, bool isdir)
> {
> struct fuse_conn *fc = fm->fc;
> struct fuse_file *ff;
> @@ -153,23 +229,41 @@ struct fuse_file *fuse_file_open(struct fuse_mount *fm, u64 nodeid,
> if (open) {
> /* Store outarg for fuse_finish_open() */
> struct fuse_open_out *outargp = &ff->args->open_outarg;
> - int err;
> + int err = -ENOSYS;
> +
> + if (inode && fc->compound_open_getattr) {
> + struct fuse_attr_out attr_outarg;
> + err = fuse_compound_open_getattr(fm, nodeid, open_flags,
> + opcode, ff, &attr_outarg, outargp);
> + if (!err)
> + fuse_change_attributes(inode, &attr_outarg.attr, NULL,
> + ATTR_TIMEOUT(&attr_outarg),
> + fuse_get_attr_version(fc));
> + }
> + if (err == -ENOSYS) {
> + err = fuse_send_open(fm, nodeid, open_flags, opcode, outargp);
>
> - err = fuse_send_open(fm, nodeid, open_flags, opcode, outargp);
> - if (!err) {
> - ff->fh = outargp->fh;
> - ff->open_flags = outargp->open_flags;
> - } else if (err != -ENOSYS) {
> - fuse_file_free(ff);
> - return ERR_PTR(err);
> - } else {
> - if (isdir) {
> + if (!err) {
> + ff->fh = outargp->fh;
> + ff->open_flags = outargp->open_flags;
> + }
> + }
> +
> + if (err) {
> + if (err != -ENOSYS) {
> + /* err is not ENOSYS */
> + fuse_file_free(ff);
> + return ERR_PTR(err);
> + } else {
> /* No release needed */
> kfree(ff->args);
> ff->args = NULL;
> - fc->no_opendir = 1;
> - } else {
> - fc->no_open = 1;
> +
> + /* we don't have open */
> + if (isdir)
> + fc->no_opendir = 1;
> + else
> + fc->no_open = 1;
> }
> }
> }
> @@ -185,11 +279,10 @@ struct fuse_file *fuse_file_open(struct fuse_mount *fm, u64 nodeid,
> int fuse_do_open(struct fuse_mount *fm, u64 nodeid, struct file *file,
> bool isdir)
> {
> - struct fuse_file *ff = fuse_file_open(fm, nodeid, file->f_flags, isdir);
> + struct fuse_file *ff = fuse_file_open(fm, nodeid, file_inode(file), file->f_flags, isdir);
>
> if (!IS_ERR(ff))
> file->private_data = ff;
> -
> return PTR_ERR_OR_ZERO(ff);
> }
> EXPORT_SYMBOL_GPL(fuse_do_open);
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index 86253517f59b..98af019037c3 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -924,6 +924,9 @@ struct fuse_conn {
> /* Use io_uring for communication */
> unsigned int io_uring;
>
> + /* Does the filesystem support compound operations? */
> + unsigned int compound_open_getattr:1;
> +
> /** Maximum stack depth for passthrough backing files */
> int max_stack_depth;
>
> @@ -1557,7 +1560,8 @@ void fuse_file_io_release(struct fuse_file *ff, struct inode *inode);
>
> /* file.c */
> struct fuse_file *fuse_file_open(struct fuse_mount *fm, u64 nodeid,
> - unsigned int open_flags, bool isdir);
> + struct inode *inode,
> + unsigned int open_flags, bool isdir);
> void fuse_file_release(struct inode *inode, struct fuse_file *ff,
> unsigned int open_flags, fl_owner_t id, bool isdir);
>
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index 819e50d66622..a5fd721be96d 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -991,6 +991,12 @@ void fuse_conn_init(struct fuse_conn *fc, struct fuse_mount *fm,
> fc->blocked = 0;
> fc->initialized = 0;
> fc->connected = 1;
> +
> + /* pretend fuse server supports compound operations
> + * until it tells us otherwise.
> + */
> + fc->compound_open_getattr = 1;
> +
> atomic64_set(&fc->attr_version, 1);
> atomic64_set(&fc->evict_ctr, 1);
> get_random_bytes(&fc->scramble_key, sizeof(fc->scramble_key));
> diff --git a/fs/fuse/ioctl.c b/fs/fuse/ioctl.c
> index fdc175e93f74..07a02e47b2c3 100644
> --- a/fs/fuse/ioctl.c
> +++ b/fs/fuse/ioctl.c
> @@ -494,7 +494,7 @@ static struct fuse_file *fuse_priv_ioctl_prepare(struct inode *inode)
> if (!S_ISREG(inode->i_mode) && !isdir)
> return ERR_PTR(-ENOTTY);
>
> - return fuse_file_open(fm, get_node_id(inode), O_RDONLY, isdir);
> + return fuse_file_open(fm, get_node_id(inode), NULL, O_RDONLY, isdir);
> }
>
> static void fuse_priv_ioctl_cleanup(struct inode *inode, struct fuse_file *ff)
>
> --
> 2.51.0
>
>
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