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ptsname.3: Fix description of failure behaviour of ptsname_r() 

The Linux man page for ptsname_r, when describing the behaviour
in the error case, is
  - not consistent with the future POSIX standard (POSIX Issue 8).
  - not consistent with musl libc.

Find attached a patch to
  - keep it consistent with what glibc does,
  - make it consistent with musl libc,
  - make it consistent with the future POSIX standard (POSIX
    Issue 8).

Details:

glibc's implementation of ptsname_r, when it fails, returns the
error code as return value AND sets errno. See
https://sourceware.org/git/?p=glibc.git;a=blob;f=login/ptsname.c
https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/mach/hurd/ptsname.c
https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/ptsname.c

musl's implementation of ptsname_r, when it fails, returns the error code
but does NOT set errno. See
https://git.musl-libc.org/cgit/musl/tree/src/misc/pty.c

The proposal to add ptsname_r to POSIX, with text

  "If successful, the ptsname_r( ) function shall return zero.
   Otherwise, an error number shall be returned to indicate the
   error."

has been accepted for inclusion in POSIX Issue 8.
http://austingroupbugs.net/view.php?id=508

Therefore a portable program should look at the return value from
ptsname_r, NOT the errno value. The current text in the man page
suggests to look at the errno value, which is wrong (because of
musl libc) and not future-proof (because of future POSIX).

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Bruno Haible 2019-01-26 14:31:56 +01:00 committed by Michael Kerrisk
parent c6364a1b33
commit 8d4d268f0e
1 changed files with 3 additions and 6 deletions
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9
man3/ptsname.3
View File

@ -63,12 +63,9 @@ On failure, NULL is returned.
On success,
.BR ptsname_r ()
returns 0.
On failure, a nonzero value is returned
and
.I errno
is set to indicate the error.
.\" In fact the errno value is also returned as the function
.\" result -- MTK, Dec 04
On failure, an error number is returned to indicate the error.
.\" In glibc, the error number is not only returned as the return value
.\" but also stored in errno. But this is not true for musl libc.
.SH ERRORS
.TP
.B EINVAL