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Date: Mon, 12 Jul 2010 10:15:29 +0200
From: Miklos Szeredi <miklos@...redi.hu>
To: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
CC: hch@...radead.org, viro@...iv.linux.org.uk, adilger@....com,
corbet@....net, neilb@...e.de, npiggin@...e.de,
hooanon05@...oo.co.jp, bfields@...ldses.org,
linux-fsdevel@...r.kernel.org, sfrench@...ibm.com,
philippe.deniel@....FR, linux-kernel@...r.kernel.org,
aneesh.kumar@...ux.vnet.ibm.com
Subject: Re: [PATCH -V16 02/12] vfs: Add name to file handle conversion support
On Mon, 12 Jul 2010, Aneesh Kumar K.V wrote:
> The file handle also include 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@...ux.vnet.ibm.com>
> ---
> fs/open.c | 124 ++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/fs.h | 9 +++
> include/linux/syscalls.h | 5 ++-
> 3 files changed, 137 insertions(+), 1 deletions(-)
>
> diff --git a/fs/open.c b/fs/open.c
> index 5463266..7ad8f28 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -29,6 +29,7 @@
> #include <linux/falloc.h>
> #include <linux/fs_struct.h>
> #include <linux/ima.h>
> +#include <linux/exportfs.h>
>
> #include "internal.h"
>
> @@ -1040,3 +1041,126 @@ int nonseekable_open(struct inode *inode, struct file *filp)
> }
>
> EXPORT_SYMBOL(nonseekable_open);
> +
> +#ifdef CONFIG_EXPORTFS
> +/* limit the handle size to some value */
> +#define MAX_HANDLE_SZ 4096
> +static long do_sys_name_to_handle(struct path *path,
> + struct file_handle __user *ufh)
> +{
> + 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;
> + /* copy the mount id */
> + handle->mnt_id = path->mnt->mnt_id;
> + 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;
> + if (copy_to_user(ufh, handle,
> + sizeof(struct file_handle) + handle_size))
> + retval = -EFAULT;
> +
> + 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
> + * @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_DEFINE4(name_to_handle_at, int, dfd, const char __user *, name,
> + struct file_handle __user *, handle, 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);
> +
> +out_path:
> + if (file)
> + fput_light(file, fput_needed);
> + else
> + path_put(&path);
> +err_out:
> + return ret;
> +}
> +#else
> +SYSCALL_DEFINE4(name_to_handle_at, int, dfd, const char __user *, name,
> + struct file_handle __user *, handle, int, flag)
> +{
> + return -ENOSYS;
> +}
> +#endif
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 471e1ff..0e7cf4c 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -949,6 +949,15 @@ struct file {
> unsigned long f_mnt_write_state;
> #endif
> };
> +
> +struct file_handle {
> + int mnt_id;
The mount id is not part of the handle in that it's not used when
converting back a handle to a file descriptor. So it shouldn't be
included here.
The uuid can be looked up based on st_dev.
> + 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 7f614ce..9d6d6e3 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -61,6 +61,7 @@ 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>
> @@ -823,5 +824,7 @@ 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 flag);
> #endif
> --
> 1.7.2.rc1
>
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