On 31.05.24 10:12, Philippe Mathieu-Daudé wrote:
On 31/5/24 10:01, David Hildenbrand wrote:
On 31.05.24 09:57, Philippe Mathieu-Daudé wrote:
Hi Michal,
On 31/5/24 09:28, Michal Privoznik wrote:
The unspoken premise of qemu_madvise() is that errno is set on
error. And it is mostly the case except for posix_madvise() which
is documented to return either zero (on success) or a positive
error number.
Watch out, Linux:
RETURN VALUE
On success, posix_madvise() returns 0. On failure,
it returns a positive error number.
but on Darwin:
RETURN VALUES
Upon successful completion, a value of 0 is returned.
Otherwise, a value of -1 is returned and errno is set
to indicate the error.
(Haven't checked other POSIX OSes).
... but it's supposed to follow the "posix standard" :D Maybe an issue
in the docs?
FreeBSD seems to follow the standard: "The posix_madvise() interface is
identical, except it returns an error number on error and does not
modify errno, and is provided for standards conformance."
Same with OpenBSD: "The posix_madvise() interface has the same effect,
but returns the error value instead of only setting errno."
On Darwin, MADVISE(2):
The posix_madvise() behaves same as madvise() except that it uses
values with POSIX_ prefix for the advice system call argument.
The posix_madvise function is part of IEEE 1003.1-2001 and was first
implemented in Mac OS X 10.2.
Per IEEE 1003.1-2001
(https://pubs.opengroup.org/onlinepubs/009695399/functions/posix_madvise.html):
RETURN VALUE
Upon successful completion, posix_madvise() shall return zero;
otherwise, an error number shall be returned to indicate the error.
Note the use of "shall" which is described in RFC2119 as:
This word, or the adjective "RECOMMENDED", mean that there
may exist valid reasons in particular circumstances to ignore a
particular item, but the full implications must be understood and
carefully weighed before choosing a different course.
Agreed, so we have to be careful.
I do wonder if there would be the option for an automatic approach: for
example, detect if the errno was/was not changed. Hm.
--
Cheers,
David / dhildenb
