chris@mimsy.UUCP (Chris Torek) (08/27/87)
Index: lib/libc/gen/isatty.c 4.3BSD Fix
Description:
Calls to isatty(), such as those in stdio, can clobber errno,
making later perror()s do strange things. There are no doubt
other library routines that do the same, but this is one of the
more obvious.
Repeat-By:
See, e.g., sendmail errors.
Fix:
I chose to change isatty() itself, rather than _flsbuf().
I doubt anything depends on errno==ENOTTY after isatty(n)==0.
RCS file: RCS/isatty.c,v
retrieving revision 1.1
retrieving revision 1.2
diff -c2 -r1.1 -r1.2
*** /tmp/,RCSt1007512 Wed Aug 26 23:13:55 1987
--- /tmp/,RCSt2007512 Wed Aug 26 23:13:55 1987
***************
*** 12,18 ****
{
struct sgttyb ttyb;
! if (ioctl(f, TIOCGETP, &ttyb) < 0)
return(0);
return(1);
}
--- 12,22 ----
{
struct sgttyb ttyb;
+ extern int errno;
+ int olderr = errno;
! if (ioctl(f, TIOCGETP, &ttyb) < 0) {
! errno = olderr;
return(0);
+ }
return(1);
}
--
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
Domain: chris@mimsy.umd.edu Path: seismo!mimsy!chrisgwyn@brl-smoke.ARPA (Doug Gwyn ) (08/27/87)
In article <8192@mimsy.UUCP> chris@mimsy.UUCP (Chris Torek) writes: > Calls to isatty(), such as those in stdio, can clobber errno, > making later perror()s do strange things. I take issue with this. By no stretch of the imagination is this a bug in isatty(); errno may always be set by successful functions, and isatty() is always successful. The real problem is programmers who invoke perror() when errno is not guaranteed to be set up correctly to indicate an error cause. By installing such a change in isatty(), you're encouraging this misuse of perror().
chris@mimsy.UUCP (Chris Torek) (08/28/87)
In article <6348@brl-smoke.ARPA> gwyn@brl-smoke.ARPA (Doug Gwyn ) writes: >... The real problem is programmers who invoke perror() when errno is >not guaranteed to be set up correctly to indicate an error cause. Agreed. Yet I think more section-3 routines should take care with errno; in particular, those routines that can fail due to failing system calls should arrange to set errno always upon failing. For instance, if ((f = fopen(tmp, "w")) == NULL) { perror("cannot create temp file"); ... is technically wrong, but most often produces what is desired. It should always produce what is desired, or there should be a better mechanism. (A global error number is rather grotty.) Restoring errno inside isatty() is not a proper fix, but may help reduce confusion until we get one. -- In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690) Domain: chris@mimsy.umd.edu Path: seismo!mimsy!chris