Ticket UUID: | 2647951 | |||
Title: | Error in exec ends stdin | |||
Type: | Bug | Version: | obsolete: 8.4.19 | |
Submitter: | eugene_cdn | Created on: | 2009-02-28 06:56:26 | |
Subsystem: | 50. Embedding Support | Assigned To: | ferrieux | |
Priority: | 5 Medium | Severity: | ||
Status: | Closed | Last Modified: | 2009-03-02 03:43:49 | |
Resolution: | Invalid | Closed By: | ferrieux | |
Closed on: | 2009-03-01 10:57:43 | |||
Description: |
Tcl version: 8.4+ OS: Linux Red Hat 4, 5 Maybe, it is a Linux bug, but it appeared in Tcl's stdin handling. I got the problem in C, but I created a Tcl script that fails the same way. If you execute a certain command though system()/exec which fails, stdin stream does not provide any more input except already buffered in C code. My Tcl script is more that 8K long because I initially got the problem on the very next byte after 8K, but attached test fails a bit earlier. Important: file must be redirected to stdin: > tclsh <xxx.tcl Read(0) just returns 0 as if it is the end of pipe/socket. If you specify file name as an argument, the script works. I cannot classify the problem. Just weird. Stdin stays open, /proc/pid/fd shows it, but 0 handle is damaged. Fork/clone is doing something bad to to the parent's stdin. Any help is appreciated. I cannot depend on any developer who can call system() and break stdin. Yes, I know that such redirection seem to make no sense, but it does; it is just a simplified version. | |||
User Comments: |
eugene_cdn added on 2009-03-02 03:43:49:
Thanks!!! ferrieux added on 2009-03-01 17:57:43: allow_comments - 1 OK got it. This is not a Tcl nor Linux problem, just one specific behavior of csh. Details from the strace: 12200 09:32:12.664493 execve("/bin/csh", ["csh"..., "-fc"..., "echo hello >fff"...], [/* 69 vars */] <unfinished ...> 12200 09:32:12.675081 dup2(0, 16) = 16 12200 09:32:12.747895 open("fff", O_WRONLY|O_CREAT|O_TRUNC, 0666) = -1 EACCES (Permission denied) 12200 09:32:12.748463 write(18, "fff: Permission denied.\n", 24) = 24 12200 09:32:12.748541 lseek(16, 0, SEEK_END) = 8660 Explanation: (1) The dup2 is part of the redirections for the "echo hello" command. It just inherits desc 0 because there is no redirection on stdin. (2) Csh tries to honour the > redirection, and gets an (expected) error. It barfs to stderr (which is okay). (3) *but* it also decides to skip ahead to the end of the local subcommand's stdin (lseek(16,...)) (4) All this hooks back to Tcl's stdin since the [exec csh] has no stdin redirection either. (5) Hence on the next attempt to read, the Tcl IO subsystem gets an EOF. QED. I have no idea why Csh does (3). At the extreme it could vaguely make sense for an interactive Csh to do that on a terminal, so that it skips to new typed command when an error has occurred in a buffered block of commands... But here the Csh is not interactive. From my seat it is a fully qualified Bug. A simple workaround is to [exec csh ... < /dev/null]. I'll thus close this artifact as Invalid, since Tcl cannot be held responsible for Csh's misbehavior. My personal take on Csh is: only use it interactively if ever. That's not a programming language. That's an engineer's nightmare. *Always* use /bin/sh when you need to resort to an OS shell. eugene_cdn added on 2009-03-01 01:55:18: File Deleted - 315599: eugene_cdn added on 2009-03-01 01:53:08: File Added - 315599: tra File Added: tra eugene_cdn added on 2009-03-01 00:33:33: File Added - 315586: tra File Added: tra ferrieux added on 2009-02-28 19:23:27: Please attach an strace: strace -f -tt -o tra tclsh < xxx.tcl eugene_cdn added on 2009-02-28 13:56:26: File Added - 315531: xxx.tcl |