Re: [LTP] [PATCH 3/4] fanotify24: Add test for FAN_PRE_ACCESS and FAN_DENY_ERRNO

[Heiko Carstens <hca@linux.ibm.com>]

On Mon, Feb 10, 2025 at 04:13:15PM +0100, Amir Goldstein wrote:
> Fork the test fanotify24 from test fanotify03, replacing the
> permission event FAN_ACCESS_PERM with the new pre-content event
> FAN_PRE_ACCESS.
> 
> The test is changed to use class FAN_CLASS_PRE_CONTENT, which is
> required for FAN_PRE_ACCESS and this class also enabled the response
> with cutomer error code FAN_DENY_ERRNO.
> 
> Unlike FAN_ACCESS_PERM, FAN_PRE_ACCESS is also created on write()
> system call.  The test case expected results are adjusted to
> respond with the default error (EPERM) to open() and write() and
> to respond with custom errors (EIO, EBUSY) to read() and execve().
> 
> Not all fs support pre-content events, so run on all filesystems
> to excercise FAN_PRE_ACCESS on all supported filesystems.
> 
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> ---
>  include/lapi/fanotify.h                       |   7 +
>  runtest/syscalls                              |   1 +
>  testcases/kernel/syscalls/fanotify/.gitignore |   1 +
>  testcases/kernel/syscalls/fanotify/fanotify.h |   3 +
>  .../kernel/syscalls/fanotify/fanotify24.c     | 433 ++++++++++++++++++
>  5 files changed, 445 insertions(+)
>  create mode 100644 testcases/kernel/syscalls/fanotify/fanotify24.c
> 
> diff --git a/include/lapi/fanotify.h b/include/lapi/fanotify.h
> index e5b930f4e..9076685e8 100644
> --- a/include/lapi/fanotify.h
> +++ b/include/lapi/fanotify.h
> @@ -124,6 +124,13 @@
>  #define FAN_EPIDFD		-2
>  #endif
>  
> +/* errno other than EPERM can specified in upper byte of deny response */
> +#ifndef FAN_DENY_ERRNO
> +#define FAN_ERRNO(err) (((((__u32)(err)) & 0xff) << 24))
> +#define FAN_DENY_ERRNO(err) (FAN_DENY | FAN_ERRNO(err))
> +#define FAN_RESPONSE_ERRNO(res) ((int)((res) >> 24))
> +#endif
> +

This does not work with latest+greatest kernel headers since there
FAN_DENY_ERRNO is defined but FAN_RESPONSE_ERRNO is not. Therefore
this ends up in a compile error:

fanotify24.c: In function ‘expected_errno’:
fanotify24.c:166:24: error: implicit declaration of function ‘FAN_RESPONSE_ERRNO’; did you mean ‘FAN_DENY_ERRNO’? [-Wimplicit-function-declaration]
  166 |                 return FAN_RESPONSE_ERRNO(response);
      |                        ^~~~~~~~~~~~~~~~~~
      |                        FAN_DENY_ERRNO

FWIW, converting the above to:

/* errno other than EPERM can specified in upper byte of deny response */
#ifndef FAN_DENY_ERRNO
#define FAN_ERRNO(err) (((((__u32)(err)) & 0xff) << 24))
#define FAN_DENY_ERRNO(err) (FAN_DENY | FAN_ERRNO(err))
#endif

#ifndef FAN_RESPONSE_ERRNO
#define FAN_RESPONSE_ERRNO(res) ((int)((res) >> 24))
#endif

works for me.

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