vfs: Add name to file handle conversion support
The syscall also return mount id which can be used
to lookup file system specific information such as uuid
in /proc/<pid>/mountinfo
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/Kconfig b/fs/Kconfig
index 3db9caa..7cb53aa 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -47,7 +47,7 @@
def_bool n
config EXPORTFS
- tristate
+ bool
config FILE_LOCKING
bool "Enable POSIX file locking API" if EXPERT
diff --git a/fs/Makefile b/fs/Makefile
index a7f7cef..ba01202 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -48,6 +48,8 @@
obj-$(CONFIG_NFS_COMMON) += nfs_common/
obj-$(CONFIG_GENERIC_ACL) += generic_acl.o
+obj-$(CONFIG_FHANDLE) += fhandle.o
+
obj-y += quota/
obj-$(CONFIG_PROC_FS) += proc/
diff --git a/fs/fhandle.c b/fs/fhandle.c
new file mode 100644
index 0000000..9f79e74
--- /dev/null
+++ b/fs/fhandle.c
@@ -0,0 +1,107 @@
+#include <linux/syscalls.h>
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/file.h>
+#include <linux/mount.h>
+#include <linux/namei.h>
+#include <linux/exportfs.h>
+#include <asm/uaccess.h>
+#include "internal.h"
+
+static long do_sys_name_to_handle(struct path *path,
+ struct file_handle __user *ufh,
+ int __user *mnt_id)
+{
+ long retval;
+ struct file_handle f_handle;
+ int handle_dwords, handle_bytes;
+ struct file_handle *handle = NULL;
+
+ /*
+ * We need t make sure wether the file system
+ * support decoding of the file handle
+ */
+ if (!path->mnt->mnt_sb->s_export_op ||
+ !path->mnt->mnt_sb->s_export_op->fh_to_dentry)
+ return -EOPNOTSUPP;
+
+ if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))
+ return -EFAULT;
+
+ if (f_handle.handle_bytes > MAX_HANDLE_SZ)
+ return -EINVAL;
+
+ handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
+ GFP_KERNEL);
+ if (!handle)
+ return -ENOMEM;
+
+ /* convert handle size to multiple of sizeof(u32) */
+ handle_dwords = f_handle.handle_bytes >> 2;
+
+ /* we ask for a non connected handle */
+ retval = exportfs_encode_fh(path->dentry,
+ (struct fid *)handle->f_handle,
+ &handle_dwords, 0);
+ handle->handle_type = retval;
+ /* convert handle size to bytes */
+ handle_bytes = handle_dwords * sizeof(u32);
+ handle->handle_bytes = handle_bytes;
+ if ((handle->handle_bytes > f_handle.handle_bytes) ||
+ (retval == 255) || (retval == -ENOSPC)) {
+ /* As per old exportfs_encode_fh documentation
+ * we could return ENOSPC to indicate overflow
+ * But file system returned 255 always. So handle
+ * both the values
+ */
+ /*
+ * set the handle size to zero so we copy only
+ * non variable part of the file_handle
+ */
+ handle_bytes = 0;
+ retval = -EOVERFLOW;
+ } else
+ retval = 0;
+ /* copy the mount id */
+ if (copy_to_user(mnt_id, &path->mnt->mnt_id, sizeof(*mnt_id)) ||
+ copy_to_user(ufh, handle,
+ sizeof(struct file_handle) + handle_bytes))
+ retval = -EFAULT;
+ kfree(handle);
+ return retval;
+}
+
+/**
+ * sys_name_to_handle_at: convert name to handle
+ * @dfd: directory relative to which name is interpreted if not absolute
+ * @name: name that should be converted to handle.
+ * @handle: resulting file handle
+ * @mnt_id: mount id of the file system containing the file
+ * @flag: flag value to indicate whether to follow symlink or not
+ *
+ * @handle->handle_size indicate the space available to store the
+ * variable part of the file handle in bytes. If there is not
+ * enough space, the field is updated to return the minimum
+ * value required.
+ */
+SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
+ struct file_handle __user *, handle, int __user *, mnt_id,
+ int, flag)
+{
+ struct path path;
+ int lookup_flags;
+ int err;
+
+ if ((flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
+ return -EINVAL;
+
+ lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
+ if (flag & AT_EMPTY_PATH)
+ lookup_flags |= LOOKUP_EMPTY;
+ err = user_path_at(dfd, name, lookup_flags, &path);
+ if (!err) {
+ err = do_sys_name_to_handle(&path, handle, mnt_id);
+ path_put(&path);
+ }
+ return err;
+}
diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
index 65afdfd..33a42f2 100644
--- a/include/linux/exportfs.h
+++ b/include/linux/exportfs.h
@@ -8,6 +8,9 @@
struct super_block;
struct vfsmount;
+/* limit the handle size to NFSv4 handle size now */
+#define MAX_HANDLE_SZ 128
+
/*
* The fileid_type identifies how the file within the filesystem is encoded.
* In theory this is freely set and parsed by the filesystem, but we try to
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b7178b0..3f64630 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -978,6 +978,13 @@
#endif
};
+struct file_handle {
+ __u32 handle_bytes;
+ int handle_type;
+ /* file identifier */
+ unsigned char f_handle[0];
+};
+
#define get_file(x) atomic_long_inc(&(x)->f_count)
#define fput_atomic(x) atomic_long_add_unless(&(x)->f_count, -1, 1)
#define file_count(x) atomic_long_read(&(x)->f_count)
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 98664db..9701126 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -62,6 +62,7 @@
struct getcpu_cache;
struct old_linux_dirent;
struct perf_event_attr;
+struct file_handle;
#include <linux/types.h>
#include <linux/aio_abi.h>
@@ -832,5 +833,7 @@
unsigned long prot, unsigned long flags,
unsigned long fd, unsigned long pgoff);
asmlinkage long sys_old_mmap(struct mmap_arg_struct __user *arg);
-
+asmlinkage long sys_name_to_handle_at(int dfd, const char __user *name,
+ struct file_handle __user *handle,
+ int __user *mnt_id, int flag);
#endif
diff --git a/init/Kconfig b/init/Kconfig
index be788c0..e72fa17 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -287,6 +287,18 @@
for processing it. A preliminary version of these tools is available
at <http://www.gnu.org/software/acct/>.
+config FHANDLE
+ bool "open by fhandle syscalls"
+ select EXPORTFS
+ help
+ If you say Y here, a user level program will be able to map
+ file names to handle and then later use the handle for
+ different file system operations. This is useful in implementing
+ userspace file servers, which now track files using handles instead
+ of names. The handle would remain the same even if file names
+ get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
+ syscalls.
+
config TASKSTATS
bool "Export task/process statistics through netlink (EXPERIMENTAL)"
depends on NET
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index c782fe9..4e01343 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -186,3 +186,6 @@
/* fanotify! */
cond_syscall(sys_fanotify_init);
cond_syscall(sys_fanotify_mark);
+
+/* open by handle */
+cond_syscall(sys_name_to_handle_at);