[PATCH v6 17/17] vfs: expose delegation support to userland

Jeff Layton
2025-11-11T14:14:03Z

Now that support for recallable directory delegations is available,
expose this functionality to userland with new F_SETDELEG and F_GETDELEG
commands for fcntl().

Note that this also allows userland to request a FL_DELEG type lease on
files too. Userland applications that do will get signalled when there
are metadata changes in addition to just data changes (which is a
limitation of FL_LEASE leases).

These commands accept a new "struct delegation" argument that contains a
flags field for future expansion.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
fs/fcntl.c | 13 +++++++++++++
fs/locks.c | 45 ++++++++++++++++++++++++++++++++++++++++-----
include/linux/filelock.h | 12 ++++++++++++
include/uapi/linux/fcntl.h | 11 +++++++++++
4 files changed, 76 insertions(+), 5 deletions(-)

diff --git a/fs/fcntl.c b/fs/fcntl.c
index 72f8433d9109889eecef56b32d20a85b4e12ea44..f93dbca0843557d197bd1e023519cfa0f00ad78f 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -445,6 +445,7 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
struct file *filp)
{
void __user *argp = (void __user *)arg;
+ struct delegation deleg;
int argi = (int)arg;
struct flock flock;
long err = -EINVAL;
@@ -550,6 +551,18 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
case F_SET_RW_HINT:
err = fcntl_set_rw_hint(filp, arg);
break;
+ case F_GETDELEG:
+ if (copy_from_user(&deleg, argp, sizeof(deleg)))
+ return -EFAULT;
+ err = fcntl_getdeleg(filp, &deleg);
+ if (!err && copy_to_user(argp, &deleg, sizeof(deleg)))
+ return -EFAULT;
+ break;
+ case F_SETDELEG:
+ if (copy_from_user(&deleg, argp, sizeof(deleg)))
+ return -EFAULT;
+ err = fcntl_setdeleg(fd, filp, &deleg);
+ break;
default:
break;
}
diff --git a/fs/locks.c b/fs/locks.c
index dd290a87f58eb5d522f03fa99d612fbad84dacf3..7f4ccc7974bc8d3e82500ee692c6520b53f2280f 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1703,7 +1703,7 @@ EXPORT_SYMBOL(lease_get_mtime);
* XXX: sfr & willy disagree over whether F_INPROGRESS
* should be returned to userspace.
*/
-int fcntl_getlease(struct file *filp)
+static int __fcntl_getlease(struct file *filp, unsigned int flavor)
{
struct file_lease *fl;
struct inode *inode = file_inode(filp);
@@ -1719,7 +1719,8 @@ int fcntl_getlease(struct file *filp)
list_for_each_entry(fl, &ctx->flc_lease, c.flc_list) {
if (fl->c.flc_file != filp)
continue;
- type = target_leasetype(fl);
+ if (fl->c.flc_flags & flavor)
+ type = target_leasetype(fl);
break;
}
spin_unlock(&ctx->flc_lock);
@@ -1730,6 +1731,19 @@ int fcntl_getlease(struct file *filp)
return type;
}

+int fcntl_getlease(struct file *filp)
+{
+ return __fcntl_getlease(filp, FL_LEASE);
+}
+
+int fcntl_getdeleg(struct file *filp, struct delegation *deleg)
+{
+ if (deleg->d_flags != 0 || deleg->__pad != 0)
+ return -EINVAL;
+ deleg->d_type = __fcntl_getlease(filp, FL_DELEG);
+ return 0;
+}
+
/**
* check_conflicting_open - see if the given file points to an inode that has
* an existing open that would conflict with the
@@ -2039,13 +2053,13 @@ vfs_setlease(struct file *filp, int arg, struct file_lease **lease, void **priv)
}
EXPORT_SYMBOL_GPL(vfs_setlease);

-static int do_fcntl_add_lease(unsigned int fd, struct file *filp, int arg)
+static int do_fcntl_add_lease(unsigned int fd, struct file *filp, unsigned int flavor, int arg)
{
struct file_lease *fl;
struct fasync_struct *new;
int error;

- fl = lease_alloc(filp, FL_LEASE, arg);
+ fl = lease_alloc(filp, flavor, arg);
if (IS_ERR(fl))
return PTR_ERR(fl);

@@ -2081,7 +2095,28 @@ int fcntl_setlease(unsigned int fd, struct file *filp, int arg)

if (arg == F_UNLCK)
return vfs_setlease(filp, F_UNLCK, NULL, (void **)&filp);
- return do_fcntl_add_lease(fd, filp, arg);
+ return do_fcntl_add_lease(fd, filp, FL_LEASE, arg);
+}
+
+/**
+ * fcntl_setdeleg - sets a delegation on an open file
+ * @fd: open file descriptor
+ * @filp: file pointer
+ * @deleg: delegation request from userland
+ *
+ * Call this fcntl to establish a delegation on the file.
+ * Note that you also need to call %F_SETSIG to
+ * receive a signal when the lease is broken.
+ */
+int fcntl_setdeleg(unsigned int fd, struct file *filp, struct delegation *deleg)
+{
+ /* For now, no flags are supported */
+ if (deleg->d_flags != 0 || deleg->__pad != 0)
+ return -EINVAL;
+
+ if (deleg->d_type == F_UNLCK)
+ return vfs_setlease(filp, F_UNLCK, NULL, (void **)&filp);
+ return do_fcntl_add_lease(fd, filp, FL_DELEG, deleg->d_type);
}

/**
diff --git a/include/linux/filelock.h b/include/linux/filelock.h
index 208d108df2d73a9df65e5dc9968d074af385f881..54b824c05299261e6bd6acc4175cb277ea35b35d 100644
--- a/include/linux/filelock.h
+++ b/include/linux/filelock.h
@@ -159,6 +159,8 @@ int fcntl_setlk64(unsigned int, struct file *, unsigned int,

int fcntl_setlease(unsigned int fd, struct file *filp, int arg);
int fcntl_getlease(struct file *filp);
+int fcntl_setdeleg(unsigned int fd, struct file *filp, struct delegation *deleg);
+int fcntl_getdeleg(struct file *filp, struct delegation *deleg);

static inline bool lock_is_unlock(struct file_lock *fl)
{
@@ -278,6 +280,16 @@ static inline int fcntl_getlease(struct file *filp)
return F_UNLCK;
}

+static inline int fcntl_setdeleg(unsigned int fd, struct file *filp, struct delegation *deleg)
+{
+ return -EINVAL;
+}
+
+static inline int fcntl_getdeleg(struct file *filp, struct delegation *deleg)
+{
+ return -EINVAL;
+}
+
static inline bool lock_is_unlock(struct file_lock *fl)
{
return false;
diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h
index 3741ea1b73d8500061567b6590ccf5fb4c6770f0..008fac15e573084a9b48e4e991528b4363c54047 100644
--- a/include/uapi/linux/fcntl.h
+++ b/include/uapi/linux/fcntl.h
@@ -79,6 +79,17 @@
*/
#define RWF_WRITE_LIFE_NOT_SET RWH_WRITE_LIFE_NOT_SET

+/* Set/Get delegations */
+#define F_GETDELEG (F_LINUX_SPECIFIC_BASE + 15)
+#define F_SETDELEG (F_LINUX_SPECIFIC_BASE + 16)
+
+/* Argument structure for F_GETDELEG and F_SETDELEG */
+struct delegation {
+ uint32_t d_flags; /* Must be 0 */
+ uint16_t d_type; /* F_RDLCK, F_WRLCK, F_UNLCK */
+ uint16_t __pad; /* Must be 0 */
+};
+
/*
* Types of directory notifications that may be requested.
*/

--
2.51.1