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Subject[PATCH -V19 02/15] vfs: Add name to file handle conversion support
Date
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>
---
fs/open.c | 129 ++++++++++++++++++++++++++++++++++++++++++++++
include/linux/exportfs.h | 3 +
include/linux/fs.h | 8 +++
include/linux/syscalls.h | 5 ++-
4 files changed, 144 insertions(+), 1 deletions(-)

diff --git a/fs/open.c b/fs/open.c
index 630715f..efb1806 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -30,6 +30,7 @@
#include <linux/fs_struct.h>
#include <linux/ima.h>
#include <linux/dnotify.h>
+#include <linux/exportfs.h>

#include "internal.h"

@@ -1042,3 +1043,131 @@ int nonseekable_open(struct inode *inode, struct file *filp)
}

EXPORT_SYMBOL(nonseekable_open);
+
+#ifdef CONFIG_EXPORTFS
+static long do_sys_name_to_handle(struct path *path,
+ struct file_handle __user *ufh,
+ int __user *mnt_id)
+{
+ long retval;
+ int handle_size;
+ struct file_handle f_handle;
+ struct file_handle *handle = NULL;
+
+ if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) {
+ retval = -EFAULT;
+ goto err_out;
+ }
+ if (f_handle.handle_size > MAX_HANDLE_SZ) {
+ retval = -EINVAL;
+ goto err_out;
+ }
+ handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_size,
+ GFP_KERNEL);
+ if (!handle) {
+ retval = -ENOMEM;
+ goto err_out;
+ }
+
+ /* convert handle size to multiple of sizeof(u32) */
+ handle_size = f_handle.handle_size >> 2;
+
+ /* we ask for a non connected handle */
+ retval = exportfs_encode_fh(path->dentry,
+ (struct fid *)handle->f_handle,
+ &handle_size, 0);
+ /* convert handle size to bytes */
+ handle_size *= sizeof(u32);
+ handle->handle_type = retval;
+ handle->handle_size = handle_size;
+ if (handle_size > f_handle.handle_size) {
+ /*
+ * set the handle_size to zero so we copy only
+ * non variable part of the file_handle
+ */
+ handle_size = 0;
+ retval = -EOVERFLOW;
+ } else
+ retval = 0;
+ /* copy the mount id */
+ if (copy_to_user(mnt_id, &path->mnt->mnt_id, sizeof(*mnt_id))) {
+ retval = -EFAULT;
+ goto err_free_out;
+ }
+ if (copy_to_user(ufh, handle,
+ sizeof(struct file_handle) + handle_size))
+ retval = -EFAULT;
+err_free_out:
+ kfree(handle);
+err_out:
+ 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)
+{
+
+ int follow;
+ int fput_needed;
+ long ret = -EINVAL;
+ struct path path, *pp;
+ struct file *file = NULL;
+
+ if ((flag & ~AT_SYMLINK_FOLLOW) != 0)
+ goto err_out;
+
+ if (name == NULL && dfd != AT_FDCWD) {
+ file = fget_light(dfd, &fput_needed);
+ if (file) {
+ pp = &file->f_path;
+ ret = 0;
+ } else
+ ret = -EBADF;
+ } else {
+ follow = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
+ ret = user_path_at(dfd, name, follow, &path);
+ pp = &path;
+ }
+ if (ret)
+ goto err_out;
+ /*
+ * We need t make sure wether the file system
+ * support decoding of the file handle
+ */
+ if (!pp->mnt->mnt_sb->s_export_op ||
+ !pp->mnt->mnt_sb->s_export_op->fh_to_dentry) {
+ ret = -EOPNOTSUPP;
+ goto out_path;
+ }
+ ret = do_sys_name_to_handle(pp, handle, mnt_id);
+
+out_path:
+ if (file)
+ fput_light(file, fput_needed);
+ else
+ path_put(&path);
+err_out:
+ return ret;
+}
+#else
+SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
+ struct file_handle __user *, handle, int __user *, mnt_id,
+ int, flag)
+{
+ return -ENOSYS;
+}
+#endif
diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
index acd0b2d..1a6d72f 100644
--- a/include/linux/exportfs.h
+++ b/include/linux/exportfs.h
@@ -8,6 +8,9 @@ struct inode;
struct super_block;
struct vfsmount;

+/* limit the handle size to some value */
+#define MAX_HANDLE_SZ 4096
+
/*
* 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 9a96b4d..f2f7ad3 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -953,6 +953,14 @@ struct file {
unsigned long f_mnt_write_state;
#endif
};
+
+struct file_handle {
+ int handle_size;
+ int handle_type;
+ /* file identifier */
+ unsigned char f_handle[0];
+};
+
extern spinlock_t files_lock;
#define file_list_lock() spin_lock(&files_lock);
#define file_list_unlock() spin_unlock(&files_lock);
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 6e5d197..f7aba76 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -62,6 +62,7 @@ struct robust_list_head;
struct getcpu_cache;
struct old_linux_dirent;
struct perf_event_attr;
+struct file_handle;

#include <linux/types.h>
#include <linux/aio_abi.h>
@@ -831,5 +832,7 @@ asmlinkage long sys_mmap_pgoff(unsigned long addr, unsigned long len,
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
--
1.7.0.4


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