Re: [PATCH v2 1/2] fuse: Add support for FUSE_SETXATTR_V2

From: Luis Henriques
Date: Mon Mar 29 2021 - 10:53:35 EST

On Thu, Mar 25, 2021 at 11:18:22AM -0400, Vivek Goyal wrote:
> Fuse client needs to send additional information to file server when
> it calls SETXATTR(system.posix_acl_access). Right now there is no extra
> space in fuse_setxattr_in. So introduce a v2 of the structure which has
> more space in it and can be used to send extra flags.
>
> "struct fuse_setxattr_in_v2" is only used if file server opts-in for it using
> flag FUSE_SETXATTR_V2 during feature negotiations.
>
> Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
> ---
> fs/fuse/acl.c | 2 +-
> fs/fuse/fuse_i.h | 5 ++++-
> fs/fuse/inode.c | 4 +++-
> fs/fuse/xattr.c | 21 +++++++++++++++------
> include/uapi/linux/fuse.h | 10 ++++++++++
> 5 files changed, 33 insertions(+), 9 deletions(-)
>
> diff --git a/fs/fuse/acl.c b/fs/fuse/acl.c
> index e9c0f916349d..d31260a139d4 100644
> --- a/fs/fuse/acl.c
> +++ b/fs/fuse/acl.c
> @@ -94,7 +94,7 @@ int fuse_set_acl(struct user_namespace *mnt_userns, struct inode *inode,
> return ret;
> }
>
> - ret = fuse_setxattr(inode, name, value, size, 0);
> + ret = fuse_setxattr(inode, name, value, size, 0, 0);
> kfree(value);
> } else {
> ret = fuse_removexattr(inode, name);
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index 63d97a15ffde..d00bf0b9a38c 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -668,6 +668,9 @@ struct fuse_conn {
> /** Is setxattr not implemented by fs? */
> unsigned no_setxattr:1;
>
> + /** Does file server support setxattr_v2 */
> + unsigned setxattr_v2:1;
> +
> /** Is getxattr not implemented by fs? */
> unsigned no_getxattr:1;
>
> @@ -1170,7 +1173,7 @@ void fuse_unlock_inode(struct inode *inode, bool locked);
> bool fuse_lock_inode(struct inode *inode);
>
> int fuse_setxattr(struct inode *inode, const char *name, const void *value,
> - size_t size, int flags);
> + size_t size, int flags, unsigned extra_flags);
> ssize_t fuse_getxattr(struct inode *inode, const char *name, void *value,
> size_t size);
> ssize_t fuse_listxattr(struct dentry *entry, char *list, size_t size);
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index b0e18b470e91..1c726df13f80 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -1052,6 +1052,8 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args,
> fc->handle_killpriv_v2 = 1;
> fm->sb->s_flags |= SB_NOSEC;
> }
> + if (arg->flags & FUSE_SETXATTR_V2)
> + fc->setxattr_v2 = 1;
> } else {
> ra_pages = fc->max_read / PAGE_SIZE;
> fc->no_lock = 1;
> @@ -1095,7 +1097,7 @@ void fuse_send_init(struct fuse_mount *fm)
> FUSE_PARALLEL_DIROPS | FUSE_HANDLE_KILLPRIV | FUSE_POSIX_ACL |
> FUSE_ABORT_ERROR | FUSE_MAX_PAGES | FUSE_CACHE_SYMLINKS |
> FUSE_NO_OPENDIR_SUPPORT | FUSE_EXPLICIT_INVAL_DATA |
> - FUSE_HANDLE_KILLPRIV_V2;
> + FUSE_HANDLE_KILLPRIV_V2 | FUSE_SETXATTR_V2;
> #ifdef CONFIG_FUSE_DAX
> if (fm->fc->dax)
> ia->in.flags |= FUSE_MAP_ALIGNMENT;
> diff --git a/fs/fuse/xattr.c b/fs/fuse/xattr.c
> index 1a7d7ace54e1..f2aae72653dc 100644
> --- a/fs/fuse/xattr.c
> +++ b/fs/fuse/xattr.c
> @@ -12,24 +12,33 @@
> #include <linux/posix_acl_xattr.h>
>
> int fuse_setxattr(struct inode *inode, const char *name, const void *value,
> - size_t size, int flags)
> + size_t size, int flags, unsigned extra_flags)
> {
> struct fuse_mount *fm = get_fuse_mount(inode);
> FUSE_ARGS(args);
> struct fuse_setxattr_in inarg;
> + struct fuse_setxattr_in_v2 inarg_v2;
> + bool setxattr_v2 = fm->fc->setxattr_v2;
> int err;
>
> if (fm->fc->no_setxattr)
> return -EOPNOTSUPP;
>
> memset(&inarg, 0, sizeof(inarg));
> - inarg.size = size;
> - inarg.flags = flags;
> + memset(&inarg_v2, 0, sizeof(inarg_v2));
> + if (setxattr_v2) {
> + inarg_v2.size = size;
> + inarg_v2.flags = flags;
> + inarg_v2.setxattr_flags = extra_flags;
> + } else {
> + inarg.size = size;
> + inarg.flags = flags;
> + }
> args.opcode = FUSE_SETXATTR;
> args.nodeid = get_node_id(inode);
> args.in_numargs = 3;
> - args.in_args[0].size = sizeof(inarg);
> - args.in_args[0].value = &inarg;
> + args.in_args[0].size = setxattr_v2 ? sizeof(inarg_v2) : sizeof(inarg);
> + args.in_args[0].value = setxattr_v2 ? &inarg_v2 : (void *)&inarg;

And yet another minor:

It's a bit awkward to have to cast '&inarg' to 'void *' just because
you're using the ternary operator. Why not use an 'if' statement instead
for initializing .size and .value?

Cheers,
--
Luís

> args.in_args[1].size = strlen(name) + 1;
> args.in_args[1].value = name;
> args.in_args[2].size = size;
> @@ -199,7 +208,7 @@ static int fuse_xattr_set(const struct xattr_handler *handler,
> if (!value)
> return fuse_removexattr(inode, name);
>
> - return fuse_setxattr(inode, name, value, size, flags);
> + return fuse_setxattr(inode, name, value, size, flags, 0);
> }
>
> static bool no_xattr_list(struct dentry *dentry)
> diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
> index 54442612c48b..1bb555c1c117 100644
> --- a/include/uapi/linux/fuse.h
> +++ b/include/uapi/linux/fuse.h
> @@ -179,6 +179,7 @@
> * 7.33
> * - add FUSE_HANDLE_KILLPRIV_V2, FUSE_WRITE_KILL_SUIDGID, FATTR_KILL_SUIDGID
> * - add FUSE_OPEN_KILL_SUIDGID
> + * - add FUSE_SETXATTR_V2
> */
>
> #ifndef _LINUX_FUSE_H
> @@ -330,6 +331,7 @@ struct fuse_file_lock {
> * does not have CAP_FSETID. Additionally upon
> * write/truncate sgid is killed only if file has group
> * execute permission. (Same as Linux VFS behavior).
> + * FUSE_SETXATTR_V2: Does file server support V2 of struct fuse_setxattr_in
> */
> #define FUSE_ASYNC_READ (1 << 0)
> #define FUSE_POSIX_LOCKS (1 << 1)
> @@ -360,6 +362,7 @@ struct fuse_file_lock {
> #define FUSE_MAP_ALIGNMENT (1 << 26)
> #define FUSE_SUBMOUNTS (1 << 27)
> #define FUSE_HANDLE_KILLPRIV_V2 (1 << 28)
> +#define FUSE_SETXATTR_V2 (1 << 29)
>
> /**
> * CUSE INIT request/reply flags
> @@ -686,6 +689,13 @@ struct fuse_setxattr_in {
> uint32_t flags;
> };
>
> +struct fuse_setxattr_in_v2 {
> + uint32_t size;
> + uint32_t flags;
> + uint32_t setxattr_flags;
> + uint32_t padding;
> +};
> +
> struct fuse_getxattr_in {
> uint32_t size;
> uint32_t padding;
> --
> 2.25.4
>