[patch] pthread_attr_setschedparam.3 : Describe EINVAL in ERRORS

[patch] pthread_attr_setschedparam.3 : Describe EINVAL in ERRORS

[Tobias Herzke]

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The following example proves that the man page 
pthread_attr_setschedparam.3 is incorrect when it claims that the 
pthread_attr_setschedparam function always succeeds on linux:

#include <pthread.h>
#include <errno.h>
int main() {
   pthread_attr_t attr;
   struct sched_param p = {-1}; /* invalid priority */
   if (pthread_attr_init(&attr) == 0)
     if (pthread_attr_setschedpolicy(&attr, SCHED_OTHER) == 0)
       if (pthread_attr_setschedparam(&attr, &p) == EINVAL)
	return 1;
   return 0;
}

The program exits with exit code 1, therefore pthread_attr_setschedparam 
has returned error code EINVAL.

I could evoke this error on ubuntu 14.04, and verify it by examining the 
eglibc-2.19 source code. The function is implemented in file 
fbtl/pthread_attr_setschedparam.c. For error checking, it calls the 
helper function check_sched_priority_attr which is implemented inline in 
file ./fbtl/pthreadP.h. This function returns EINVAL if a range check fails.

The attached patch corrects the man page. The patch is against the 
current git master, 298f72af973e4bf3975d6a84369286b548e6fb63


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diff --git a/man3/pthread_attr_setschedparam.3 b/man3/pthread_attr_setschedparam.3
index f3db870..8ea4f47 100644
--- a/man3/pthread_attr_setschedparam.3
+++ b/man3/pthread_attr_setschedparam.3
@@ -86,15 +86,22 @@ to
 On success, these functions return 0;
 on error, they return a nonzero error number.
 .SH ERRORS
-POSIX.1 documents
+.BR pthread_attr_setschedparam ()
+can fail with the following error:
+.TP
 .B EINVAL
-and
+the priority specified in
+.I param
+does not make sense for the current scheduling policy of
+.IR attr .
+.PP
+POSIX.1 also documents an
 .B ENOTSUP
-errors for
+error for
 .BR pthread_attr_setschedparam ().
-On Linux these functions always succeed
+This value is never returned on Linux
 (but portable and future-proof applications should nevertheless
-handle a possible error return).
+handle this error return value).
 .\" .SH VERSIONS
 .\" Available since glibc 2.0.
 .SH ATTRIBUTES

Re: [patch] pthread_attr_setschedparam.3 : Describe EINVAL in ERRORS

[Michael Kerrisk (man-pages)]

On 10/11/2014 09:04 PM, Tobias Herzke wrote:
> The following example proves that the man page 
> pthread_attr_setschedparam.3 is incorrect when it claims that the 
> pthread_attr_setschedparam function always succeeds on linux:
> 
> #include <pthread.h>
> #include <errno.h>
> int main() {
>    pthread_attr_t attr;
>    struct sched_param p = {-1}; /* invalid priority */
>    if (pthread_attr_init(&attr) == 0)
>      if (pthread_attr_setschedpolicy(&attr, SCHED_OTHER) == 0)
>        if (pthread_attr_setschedparam(&attr, &p) == EINVAL)
> 	return 1;
>    return 0;
> }
> 
> The program exits with exit code 1, therefore pthread_attr_setschedparam 
> has returned error code EINVAL.
> 
> I could evoke this error on ubuntu 14.04, and verify it by examining the 
> eglibc-2.19 source code. The function is implemented in file 
> fbtl/pthread_attr_setschedparam.c. For error checking, it calls the 
> helper function check_sched_priority_attr which is implemented inline in 
> file ./fbtl/pthreadP.h. This function returns EINVAL if a range check fails.
> 
> The attached patch corrects the man page. The patch is against the 
> current git master, 298f72af973e4bf3975d6a84369286b548e6fb63

Thanks, Tobias.

Patch applied.

Cheers,

Michael

=====
diff --git a/man3/pthread_attr_setschedparam.3 b/man3/pthread_attr_setschedparam.3
index f3db870..8ea4f47 100644
--- a/man3/pthread_attr_setschedparam.3
+++ b/man3/pthread_attr_setschedparam.3
@@ -86,15 +86,22 @@ to
 On success, these functions return 0;
 on error, they return a nonzero error number.
 .SH ERRORS
-POSIX.1 documents
+.BR pthread_attr_setschedparam ()
+can fail with the following error:
+.TP
 .B EINVAL
-and
+the priority specified in
+.I param
+does not make sense for the current scheduling policy of
+.IR attr .
+.PP
+POSIX.1 also documents an
 .B ENOTSUP
-errors for
+error for
 .BR pthread_attr_setschedparam ().
-On Linux these functions always succeed
+This value is never returned on Linux
 (but portable and future-proof applications should nevertheless
-handle a possible error return).
+handle this error return value).
 .\" .SH VERSIONS
 .\" Available since glibc 2.0.
 .SH ATTRIBUTES


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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