Re: [Qemu-devel] [PATCH v2] linux-user: add name_to_handle_at/open_by_handle_at

[Riku Voipio <riku.voipio@iki.fi>]

On Tue, Sep 01, 2015 at 10:27:33PM +0200, Laurent Vivier wrote:
> This patch allows to run example given by open_by_handle_at(2):
> 
>       The following shell session demonstrates the use of these two programs:
> 
>            $ echo 'Can you please think about it?' > cecilia.txt
>            $ ./t_name_to_handle_at cecilia.txt > fh
>            $ ./t_open_by_handle_at < fh
>            open_by_handle_at: Operation not permitted
>            $ sudo ./t_open_by_handle_at < fh      # Need CAP_SYS_ADMIN
>            Read 31 bytes
>            $ rm cecilia.txt
> 
>        Now  we delete and (quickly) re-create the file so that it has the same
>        content and (by chance) the  same  inode.[...]
> 
>            $ stat --printf="%i\n" cecilia.txt     # Display inode number
>            4072121
>            $ rm cecilia.txt
>            $ echo 'Can you please think about it?' > cecilia.txt
>            $ stat --printf="%i\n" cecilia.txt     # Check inode number
>            4072121
>            $ sudo ./t_open_by_handle_at < fh
>            open_by_handle_at: Stale NFS file handle
> 
> See the man page for source code.

Applied to linux-user,
Thanks

> Signed-off-by: Laurent Vivier <laurent@vivier.eu>
> ---
> v2: Rename function parameters, swap fh->handle_type in both functions,
>     When I have re-tested the patch I have found a bug in the size of
>     the data, so I fix this too (handle_bytes is the size of f_handle[]
>     only, not of the whole structure)
> 
>  linux-user/syscall.c | 98 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 98 insertions(+)
> 
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index f62c698..8a17351 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -5246,6 +5246,94 @@ static int do_futex(target_ulong uaddr, int op, int val, target_ulong timeout,
>          return -TARGET_ENOSYS;
>      }
>  }
> +#if defined(TARGET_NR_name_to_handle_at) && defined(CONFIG_OPEN_BY_HANDLE)
> +static abi_long do_name_to_handle_at(abi_long dirfd, abi_long pathname,
> +                                     abi_long handle, abi_long mount_id,
> +                                     abi_long flags)
> +{
> +    struct file_handle *target_fh;
> +    struct file_handle *fh;
> +    int mid = 0;
> +    abi_long ret;
> +    char *name;
> +    unsigned int size, total_size;
> +
> +    if (get_user_s32(size, handle)) {
> +        return -TARGET_EFAULT;
> +    }
> +
> +    name = lock_user_string(pathname);
> +    if (!name) {
> +        return -TARGET_EFAULT;
> +    }
> +
> +    total_size = sizeof(struct file_handle) + size;
> +    target_fh = lock_user(VERIFY_WRITE, handle, total_size, 0);
> +    if (!target_fh) {
> +        unlock_user(name, pathname, 0);
> +        return -TARGET_EFAULT;
> +    }
> +
> +    fh = g_malloc0(total_size);
> +    fh->handle_bytes = size;
> +
> +    ret = get_errno(name_to_handle_at(dirfd, path(name), fh, &mid, flags));
> +    unlock_user(name, pathname, 0);
> +
> +    /* man name_to_handle_at(2):
> +     * Other than the use of the handle_bytes field, the caller should treat
> +     * the file_handle structure as an opaque data type
> +     */
> +
> +    memcpy(target_fh, fh, total_size);
> +    target_fh->handle_bytes = tswap32(fh->handle_bytes);
> +    target_fh->handle_type = tswap32(fh->handle_type);
> +    g_free(fh);
> +    unlock_user(target_fh, handle, total_size);
> +
> +    if (put_user_s32(mid, mount_id)) {
> +        return -TARGET_EFAULT;
> +    }
> +
> +    return ret;
> +
> +}
> +#endif
> +
> +#if defined(TARGET_NR_open_by_handle_at) && defined(CONFIG_OPEN_BY_HANDLE)
> +static abi_long do_open_by_handle_at(abi_long mount_fd, abi_long handle,
> +                                     abi_long flags)
> +{
> +    struct file_handle *target_fh;
> +    struct file_handle *fh;
> +    unsigned int size, total_size;
> +    abi_long ret;
> +
> +    if (get_user_s32(size, handle)) {
> +        return -TARGET_EFAULT;
> +    }
> +
> +    total_size = sizeof(struct file_handle) + size;
> +    target_fh = lock_user(VERIFY_READ, handle, total_size, 1);
> +    if (!target_fh) {
> +        return -TARGET_EFAULT;
> +    }
> +
> +    fh = g_malloc0(total_size);
> +    memcpy(fh, target_fh, total_size);
> +    fh->handle_bytes = size;
> +    fh->handle_type = tswap32(target_fh->handle_type);
> +
> +    ret = get_errno(open_by_handle_at(mount_fd, fh,
> +                    target_to_host_bitmask(flags, fcntl_flags_tbl)));
> +
> +    g_free(fh);
> +
> +    unlock_user(target_fh, handle, total_size);
> +
> +    return ret;
> +}
> +#endif
>  
>  /* Map host to target signal numbers for the wait family of syscalls.
>     Assume all other status bits are the same.  */
> @@ -5655,6 +5743,16 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
>                                    arg4));
>          unlock_user(p, arg2, 0);
>          break;
> +#if defined(TARGET_NR_name_to_handle_at) && defined(CONFIG_OPEN_BY_HANDLE)
> +    case TARGET_NR_name_to_handle_at:
> +        ret = do_name_to_handle_at(arg1, arg2, arg3, arg4, arg5);
> +        break;
> +#endif
> +#if defined(TARGET_NR_open_by_handle_at) && defined(CONFIG_OPEN_BY_HANDLE)
> +    case TARGET_NR_open_by_handle_at:
> +        ret = do_open_by_handle_at(arg1, arg2, arg3);
> +        break;
> +#endif
>      case TARGET_NR_close:
>          ret = get_errno(close(arg1));
>          break;
> -- 
> 2.4.3
> 
>