On 20-05-22 16:47:19, Al Viro wrote:
Hello Al,
Thank you for review. This is going to be an invaluable learning for
experience me. Also, apologies for causing you to do more work.
[...]
> Now ask yourself what might be the reason for that "duplicated argument".
> Try to figure out what the values of those constants might depend upon.
> For extra points, try to guess what has caused the divergences.
>
> Please, post the result of your investigation in followup to this.
I had a look at O_NONBLOCK and O_NDELAY, and the values of these are
platform-specific, as per:
include/uapi/asm-generic/fcntl.h:
#define O_NONBLOCK 00004000
#define O_NDELAY O_NONBLOCK
arch/sparc/include/uapi/asm/fcntl.h:
#define O_NONBLOCK 0x4000
#if defined(__sparc__) && defined(__arch64__)
#define O_NDELAY 0x0004
#else
#define O_NDELAY (0x0004 | O_NONBLOCK)
#endif
arch/alpha/include/uapi/asm/fcntl.h:
#define O_NONBLOCK 00004
arch/mips/include/uapi/asm/fcntl.h:
#define O_NONBLOCK 0x0080
For Sparc, there we handle it as a special case, for example:
linux/fs/ioctl.c ->
ioctl_fionbio():
#ifdef __sparc__
/* SunOS compatibility item. */
if (O_NONBLOCK != O_NDELAY)
flag |= O_NDELAY;
#endif
There is also a comment in the fs/fcntl.c that adds clarification:
fs/fcntl.c ->
fcntl_init():
/*
* Please add new bits here to ensure allocation uniqueness.
* Exceptions: O_NONBLOCK is a two bit define on parisc; O_NDELAY
* is defined as O_NONBLOCK on some platforms and not on others.
*/
The behaviour of O_NONBLOCK and O_NDELAY also is platform-dependent,
where O_NDELAY might just return 0 instead of returning an error and
setting errno to either EAGAIN or EWOULDBLOCK.
I also took a look at commit 80f18379a7c3 ("fs: add a VALID_OPEN_FLAGS")
that introduced the new definition.
After looking at the warning coming from Coccinelle, I had a look and
assumed that flag O_NDELAY was added to the VALID_OPEN_FLAGS twice
accidentally.
I am still unsure why we would want to keep O_NDELAY twice? Setting the
same bits multiple would be a non-operation to the best of my knowledge.
But, I sincerely apologise for a not very clear commit message and not
mentioning the flag in the subject and explaining what has been done
better. I will send a v2, if that is OK with you?
Again, thank you for you time!
Krzysztof
