On Tue, Oct 25, 2016 at 12:13:51PM -0500, Eduardo Bustamante wrote: > I see the change was introduced here > http://git.kernel.org/cgit/utils/dash/dash.git/commit/?id=f78674ed6f95b594dcac0e96d6a76c5f64aa2cbf, > by importing code from FreeBSD's sh.
> What I find interesting is testing the contents of 'sb', when the > fstat64 call failed. FreeBSD's code has the opposite: > https://github.com/freebsd/freebsd/blob/master/bin/sh/redir.c#L200, > i.e. they do: > if (fstat(f, &sb) != -1 && S_ISREG(sb.st_mode)) { > BTW, that code was introduced here: > https://github.com/freebsd/freebsd/commit/e3cb9d1015e8283f4f9d116cf50f510741f8c0dd The FreeBSD code is how it was intended to be. I don't know how the dash bug was introduced. The bug only appears when a parallel actor replaces an openable non-regular file (such as a symlink to /dev/null) with a regular file and may cause corruption of the file. As noted on austin-group-l recently, the code does suffer from an issue where a noclobber open may fail if a parallel actor deletes a non-regular file (stat reports non-regular file, open fails). Many other shells have this issue, though. > Also, the way the open is performed has an interesting consequence, > i.e. the redirection operation on a FIFO blocks until something is > written to the FIFO: > hp% dash -Cc 'rm ff; mkfifo ff; echo a > ff' > ^Cdash: 1: cannot create ff: Interrupted system call > It seems to be the same case for mksh, ksh93, posh, pdksh. Not that it > matters though. Blocking is intended behaviour when opening a fifo without a counterparty. It can be used to good effect for synchronizing processes, sometimes even without transferring any data. -- Jilles Tjoelker -- To unsubscribe from this list: send the line "unsubscribe dash" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
