From 3df604a4be76db6ccf285eda6b4b3f5f6ec7497d Mon Sep 17 00:00:00 2001 From: Peter Stephenson Date: Tue, 9 Jun 2020 18:04:46 +0100 Subject: 46026: Add CLOBBER_EMPTY option. --- Src/exec.c | 27 ++++++++++++++++++++++----- 1 file changed, 22 insertions(+), 5 deletions(-) (limited to 'Src/exec.c') diff --git a/Src/exec.c b/Src/exec.c index c72d485b2..045b5d2b9 100644 --- a/Src/exec.c +++ b/Src/exec.c @@ -2143,14 +2143,15 @@ clobber_open(struct redir *f) { struct stat buf; int fd, oerrno; + char *ufname = unmeta(f->name); /* If clobbering, just open. */ if (isset(CLOBBER) || IS_CLOBBER_REDIR(f->type)) - return open(unmeta(f->name), + return open(ufname, O_WRONLY | O_CREAT | O_TRUNC | O_NOCTTY, 0666); /* If not clobbering, attempt to create file exclusively. */ - if ((fd = open(unmeta(f->name), + if ((fd = open(ufname, O_WRONLY | O_CREAT | O_EXCL | O_NOCTTY, 0666)) >= 0) return fd; @@ -2158,11 +2159,27 @@ clobber_open(struct redir *f) * Try opening, and if it's a regular file then close it again * * because we weren't supposed to open it. */ oerrno = errno; - if ((fd = open(unmeta(f->name), O_WRONLY | O_NOCTTY)) != -1) { - if(!fstat(fd, &buf) && !S_ISREG(buf.st_mode)) - return fd; + if ((fd = open(ufname, O_WRONLY | O_NOCTTY)) != -1) { + if(!fstat(fd, &buf)) { + if (!S_ISREG(buf.st_mode)) + return fd; + /* + * If CLOBBER_EMPTY is in effect and the file is empty, + * we are allowed to re-use it. + * + * Note: there is an intrinsic race here because another + * process can write to this file at any time. The only fix + * would be file locking, which we wish to avoid in basic + * file operations at this level. This would not be + * fixed. just additionally complicated, by re-opening the + * file and truncating. + */ + if (isset(CLOBBEREMPTY) && buf.st_size == 0) + return fd; + } close(fd); } + errno = oerrno; return -1; } -- cgit 1.4.1