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Commit 990d6c2d authored by Aneesh Kumar K.V's avatar Aneesh Kumar K.V Committed by Al Viro
Browse files

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: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent f52e0c11

fs/Kconfig

+1 −1
Original line number Diff line number Diff line
@@ -47,7 +47,7 @@ config FS_POSIX_ACL 
	def_bool n



config EXPORTFS

	tristate

	bool



config FILE_LOCKING

	bool "Enable POSIX file locking API" if EXPERT

fs/Makefile

+2 −0
Original line number Diff line number Diff line
@@ -48,6 +48,8 @@ obj-$(CONFIG_FS_POSIX_ACL) += posix_acl.o xattr_acl.o 
obj-$(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/

fs/fhandle.c

0 → 100644
+107 −0
Original line number Diff line number Diff line 
#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;

}

include/linux/exportfs.h

+3 −0
Original line number Diff line number Diff line
@@ -8,6 +8,9 @@ struct inode; 
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

include/linux/fs.h

+7 −0
Original line number Diff line number Diff line
@@ -978,6 +978,13 @@ struct file { 
#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)