Re: [PATCH 2/2] git: continue alias lookup on EACCES errors

From: Jeff King <peff@peff.net>
Date: Mar 28, 2012, 20:51 UTC
Message-ID: <20120328205144.GA10174@sigill.intra.peff.net>
In-Reply-To: <20120328204221.GE8982@burratino>

On Wed, Mar 28, 2012 at 03:42:21PM -0500, Jonathan Nieder wrote:

> > +		path = mkpath("%.*s/%s", (int)(end - p), p, file);
> [...]
>  - (end - p) is not guaranteed to fit inside an int.  What should happen
>    when my PATH is very long?

That is the cost of using the mkpath convenience function (otherwise, the compiler will complain that ".*" expects an int). We can do it manually, but in practice, do you really expect your PATH environment variable to overflow an int?

>  - the existence check would be simpler spelled as access(path, F_OK).

Yeah, I think that is nicer. I went with !stat() because that is our usual file_exists test, and I was wondering if there were any portability issues with access(..., F_OK). However, we seem to use it already in other places, so it should be fine.

>  - the above checks if there is _any_ nonexecutable instance of "file"
>    in the directories listed in $PATH, but isn't what we want to check
>    whether _all_ of them are nonexecutable?

If there is one that is executable, then execvp would not have returned. So if there is any entry that is non-executable, then they all are. And we don't care about the actual number; we only care whether there is one (in which case it is no ENOENT).

Show 14 quoted lines

> > +int sane_execvp(const char *file, char * const argv[])
> > +{
> > +	int ret = execvp(file, argv);
> > +	if (ret < 0 && errno == EACCES && !file_in_path_is_nonexecutable(file))
> > +		errno = ENOENT;
> > +	return ret;
> > +}
> 
> Makes sense.  No objections from me.
> 
> 	if (!execvp(file, argv))
> 		return 0;
> [...]
> 	return -1;

That is nicer; I have a general avoidance of rewriting return codes, but I think it is safe to translate a non-zero execvp result into -1.

Show 9 quoted lines

> 	/*
> 	 * When a command can't be found because one of the directories
> 	 * listed in $PATH is unsearchable, execvp reports EACCES, but
> 	 * careful usability testing (read: analysis of occasional bug
> 	 * reports) reveals that "No such file or directory" is more
> 	 * intuitive.
> 	 */
> 	if (errno == EACCES && cannot_find_in_PATH(file))
> 		errno = ENOENT;

I think we can even simplify cannot_find to "!exists_in_PATH" to make it even simpler. If it exists and execvp did not execute it, then it must be non-executable (or there is a race condition :) ).

-Peff