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Wong" , Randy Dunlap , Jeff Layton , Amir Goldstein , Jonathan Cameron , Stefan Hajnoczi , Joanne Koong , Josef Bacik , Bagas Sanjaya , Chen Linxuan , James Morse , Fuad Tabba , Sean Christopherson , Shivank Garg , Ackerley Tng , Gregory Price , Aravind Ramesh , Ajay Joshi , venkataravis@micron.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, linux-fsdevel@vger.kernel.org, John Groves Subject: [PATCH V3 3/4] fuse: add API to set kernel mount options Date: Wed, 7 Jan 2026 09:34:42 -0600 Message-ID: <20260107153443.64794-4-john@groves.net> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20260107153443.64794-1-john@groves.net> References: <20260107153244.64703-1-john@groves.net> <20260107153443.64794-1-john@groves.net> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Add fuse_add_kernel_mount_opt() to allow libfuse callers to pass additional mount options directly to the kernel. This enables filesystem-specific kernel mount options that aren't exposed through the standard libfuse mount option parsing. For example, famfs uses this to set the "shadow=" mount option for shadow file system mounts. API addition: int fuse_add_kernel_mount_opt(struct fuse_session *se, const char *mount_opt) Signed-off-by: John Groves --- include/fuse_lowlevel.h | 10 ++++++++++ lib/fuse_i.h | 1 + lib/fuse_lowlevel.c | 5 +++++ lib/fuse_versionscript | 1 + lib/mount.c | 8 ++++++++ 5 files changed, 25 insertions(+) diff --git a/include/fuse_lowlevel.h b/include/fuse_lowlevel.h index 016f831..d2bbcca 100644 --- a/include/fuse_lowlevel.h +++ b/include/fuse_lowlevel.h @@ -2195,6 +2195,16 @@ static inline int fuse_session_custom_io(struct fuse_session *se, } #endif +/** + * Allow a libfuse caller to directly add kernel mount opts + * + * @param se session object + * @param mount_opt the option to add + * + * @return 0 on success, -1 on failure + */ +int fuse_add_kernel_mount_opt(struct fuse_session *se, const char *mount_opt); + /** * Mount a FUSE file system. * diff --git a/lib/fuse_i.h b/lib/fuse_i.h index 65d2f68..41285d2 100644 --- a/lib/fuse_i.h +++ b/lib/fuse_i.h @@ -220,6 +220,7 @@ void destroy_mount_opts(struct mount_opts *mo); void fuse_mount_version(void); unsigned get_max_read(struct mount_opts *o); void fuse_kern_unmount(const char *mountpoint, int fd); +int __fuse_add_kernel_mount_opt(struct fuse_session *se, const char *mount_opt); int fuse_kern_mount(const char *mountpoint, struct mount_opts *mo); int fuse_send_reply_iov_nofree(fuse_req_t req, int error, struct iovec *iov, diff --git a/lib/fuse_lowlevel.c b/lib/fuse_lowlevel.c index 0cde3d4..413e7c3 100644 --- a/lib/fuse_lowlevel.c +++ b/lib/fuse_lowlevel.c @@ -4349,6 +4349,11 @@ int fuse_session_custom_io_30(struct fuse_session *se, offsetof(struct fuse_custom_io, clone_fd), fd); } +int fuse_add_kernel_mount_opt(struct fuse_session *se, const char *mount_opt) +{ + return __fuse_add_kernel_mount_opt(se, mount_opt); +} + int fuse_session_mount(struct fuse_session *se, const char *_mountpoint) { int fd; diff --git a/lib/fuse_versionscript b/lib/fuse_versionscript index f9562b6..536569a 100644 --- a/lib/fuse_versionscript +++ b/lib/fuse_versionscript @@ -220,6 +220,7 @@ FUSE_3.18 { fuse_reply_statx; fuse_fs_statx; + fuse_add_kernel_mount_opt; } FUSE_3.17; FUSE_3.19 { diff --git a/lib/mount.c b/lib/mount.c index 7a856c1..e6c2305 100644 --- a/lib/mount.c +++ b/lib/mount.c @@ -674,6 +674,14 @@ void destroy_mount_opts(struct mount_opts *mo) free(mo); } +int __fuse_add_kernel_mount_opt(struct fuse_session *se, const char *mount_opt) +{ + if (!se->mo) + return -1; + if (!mount_opt) + return -1; + return fuse_opt_add_opt(&se->mo->kernel_opts, mount_opt); +} int fuse_kern_mount(const char *mountpoint, struct mount_opts *mo) { -- 2.49.0