vfs: expose delegation support to userland

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>
Link: https://patch.msgid.link/20251111-dir-deleg-ro-v6-17-52f3feebb2f2@kernel.org
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/fcntl.c b/fs/fcntl.c
index 72f8433d9109889eecef56b32d20a85b4e12ea44..f93dbca0843557d197bd1e023519cfa0f00ad78f 100644 (file)
--- 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 (file)
--- 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 (file)
--- 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 (file)
--- 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.
  */