* 3.4.6-1 shm_open always returns -1, errno EINVAL
@ 2023-03-12 6:44 Matthew Rickard
2023-03-12 10:35 ` Csaba Raduly
0 siblings, 1 reply; 4+ messages in thread
From: Matthew Rickard @ 2023-03-12 6:44 UTC (permalink / raw)
To: cygwin
Hi all,
Cygwin 3.4.6-1 shm_open seems to reject all calls, returning the value
-1 and setting errno to 22 EINVAL.
For example, this program:
#include <sys/mman.h>
#include <fcntl.h>
#include <errno.h>
#include <stdio.h>
int main() {
int res = shm_open("123", O_CREAT | O_RDWR, 0666);
int error = errno;
printf("res=%d errno=%d\n", res, errno);
if (error == EINVAL)
printf("That's EINVAL\n");
return 0;
}
Says:
$ gcc -Og -o tiny tiny.c; ./tiny
res=-1 errno=22
That's EINVAL
Not sure if relevant, but I am currently running cygserver, with a
default config.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: 3.4.6-1 shm_open always returns -1, errno EINVAL
2023-03-12 6:44 3.4.6-1 shm_open always returns -1, errno EINVAL Matthew Rickard
@ 2023-03-12 10:35 ` Csaba Raduly
2023-03-12 22:55 ` Matthew Rickard
0 siblings, 1 reply; 4+ messages in thread
From: Csaba Raduly @ 2023-03-12 10:35 UTC (permalink / raw)
To: Matthew Rickard, cygwin list
Hi Matthew,
On Sun, 12 Mar 2023 at 07:44, Matthew Rickard wrote:
>
> Hi all,
>
> Cygwin 3.4.6-1 shm_open seems to reject all calls, returning the value
> -1 and setting errno to 22 EINVAL.
>
> For example, this program:
>
> #include <sys/mman.h>
> #include <fcntl.h>
> #include <errno.h>
> #include <stdio.h>
>
> int main() {
> int res = shm_open("123", O_CREAT | O_RDWR, 0666);
> int error = errno;
> printf("res=%d errno=%d\n", res, errno);
> if (error == EINVAL)
> printf("That's EINVAL\n");
> return 0;
> }
>
> Says:
>
> $ gcc -Og -o tiny tiny.c; ./tiny
> res=-1 errno=22
> That's EINVAL
>
https://man7.org/linux/man-pages/man3/shm_open.3.html says:
For portable use, a shared memory object should be identified by
a name of the form /somename; that is, a null-terminated string
of up to NAME_MAX (i.e., 255) characters consisting of an initial
slash, followed by one or more characters, none of which are
slashes.
Changing the shm_open call to
shm_open("/123", O_CREAT | O_RDWR, 0666);
returns 3 and sets errno to zero.
Csaba
--
You can get very substantial performance improvements
by not doing the right thing. - Scott Meyers, An Effective C++11/14 Sampler
So if you're looking for a completely portable, 100% standards-conformant way
to get the wrong information: this is what you want. - Scott Meyers (C++TDaWYK)
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: 3.4.6-1 shm_open always returns -1, errno EINVAL
2023-03-12 10:35 ` Csaba Raduly
@ 2023-03-12 22:55 ` Matthew Rickard
2023-03-13 15:07 ` [EXTERNAL] " Lavrentiev, Anton (NIH/NLM/NCBI) [C]
0 siblings, 1 reply; 4+ messages in thread
From: Matthew Rickard @ 2023-03-12 22:55 UTC (permalink / raw)
To: Csaba Raduly, cygwin list
That's perfect, thank you!
On 12/03/2023 9:35 pm, Csaba Raduly wrote:
> Hi Matthew,
...
> https://man7.org/linux/man-pages/man3/shm_open.3.html says:
>
> For portable use, a shared memory object should be identified by
> a name of the form /somename; that is, a null-terminated string
> of up to NAME_MAX (i.e., 255) characters consisting of an initial
> slash, followed by one or more characters, none of which are
> slashes.
>
> Changing the shm_open call to
>
> shm_open("/123", O_CREAT | O_RDWR, 0666);
>
> returns 3 and sets errno to zero.
>
> Csaba
^ permalink raw reply [flat|nested] 4+ messages in thread
* RE: [EXTERNAL] Re: 3.4.6-1 shm_open always returns -1, errno EINVAL
2023-03-12 22:55 ` Matthew Rickard
@ 2023-03-13 15:07 ` Lavrentiev, Anton (NIH/NLM/NCBI) [C]
0 siblings, 0 replies; 4+ messages in thread
From: Lavrentiev, Anton (NIH/NLM/NCBI) [C] @ 2023-03-13 15:07 UTC (permalink / raw)
To: Matthew Rickard, Csaba Raduly, cygwin list
> > returns 3 and sets errno to zero.
Note that "setting errno to zero" is not guaranteed in case of a successful completion of a library function or a system call.
Generally, "errno" reflects an error that occurred last when such a call failed (so in other words, in case of a successful
completion, "errno" can still carry over an error from a previously failed call). In this particular use case, it looks like
"errno" was clear from the get go because nothing was called prior to "shm_open()", and so it remained so when the call returned (successfully).
HTH,
Anton Lavrentiev
Contractor NIH/NLM/NCBI
^ permalink raw reply [flat|nested] 4+ messages in thread
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2023-03-12 6:44 3.4.6-1 shm_open always returns -1, errno EINVAL Matthew Rickard
2023-03-12 10:35 ` Csaba Raduly
2023-03-12 22:55 ` Matthew Rickard
2023-03-13 15:07 ` [EXTERNAL] " Lavrentiev, Anton (NIH/NLM/NCBI) [C]
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