https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=241559
Bug ID: 241559
Summary: cat(1) endless loop when writing to special device
file
Product: Base System
Version: 12.1-RELEASE
Hardware: Any
OS: Any
Status: New
Severity: Affects Only Me
Priority: ---
Component: bin
Assignee: b...@freebsd.org
Reporter: sig...@gmail.com
Using cat to write to a disk directly loops forever when it reaches the end of
the disk and there's still data to write (like when using /dev/zero or
/dev/random for example). write() returns 0 (without setting errno) when that
happens (one of the very rare cases where that can happen it seems) and cat
handles this by retrying the write forever. It would be better to error out in
this case AFAIK. There must be tons of programs that react very poorly when
making them write to a device file directly like that, but one might expect
that cat always work (more or less).
$ mdconfig -s 1m -u 10
$ cat /dev/zero > /dev/md10 # loops forever
cp seems to handle it better:
$ cp /dev/zero /dev/md10
cp: /dev/md10: No error: 0
Which isn't a very good error message but still better since it doesn't loop
forever.
With this change:
Index: bin/cat/cat.c
===================================================================
--- bin/cat/cat.c (revision 354128)
+++ bin/cat/cat.c (working copy)
@@ -327,7 +327,7 @@
}
while ((nr = read(rfd, buf, bsize)) > 0)
for (off = 0; nr; nr -= nw, off += nw)
- if ((nw = write(wfd, buf + off, (size_t)nr)) < 0)
+ if ((nw = write(wfd, buf + off, (size_t)nr)) <= 0)
err(1, "stdout");
if (nr < 0) {
warn("%s", filename);
It errors out like cp instead:
$ cat /dev/zero > /dev/md10
cat: stdout: No error: 0
That's when cat is in "raw mode". In "cooked mode", it already errors out, but
it picks up a bogus errno for it:
$ cat -v /dev/zero > /dev/md10
cat: stdout: Inappropriate ioctl for device
Which comes from an isatty() call in stdio. errno should be saved at some
point, dunno if it should be done by cat or stdio (before its call to isatty()
in __smakebuf()). Not very important though I guess.
--
You are receiving this mail because:
You are the assignee for the bug.
_______________________________________________
freebsd-bugs@freebsd.org mailing list
https://lists.freebsd.org/mailman/listinfo/freebsd-bugs
To unsubscribe, send any mail to "freebsd-bugs-unsubscr...@freebsd.org"
