[PATCH 4/4] config.c: rewrite ENODEV into EISDIR when mmap fails

From: Jeff King <peff@peff.net>
Date: May 28, 2015, 08:03 UTC
Message-ID: <20150528080300.GD23395@peff.net>
In-Reply-To: <20150528075142.GB3688@peff.net>

If we try to mmap a directory, we'll get ENODEV. This translates to "no such device" for the user, which is not very helpful. Since we've just fstat()'d the file, we can easily check whether the problem was a directory to give a better message.

Signed-off-by: Jeff King <peff@peff.net>
---
It feels a bit wrong to put this magic conversion here, and not in
xmmap. But of course xmmap does not have the stat information.

Which makes me wonder if we should provide an interface that will take the whole "struct stat" rather than just the size. That's less flexible, but in most cases, we're mapping the whole file (the packfiles are the big exception, where we use a window).

We could also potentially drop some of the useless options. As of patch 1, all of our calls are PROT_READ. They must all be MAP_PRIVATE, or our pread compatibility wrapper will fail, and we never use other flags. We never request a specific address. And in a whole-file remap, the offset will always be 0. So something like:

  void *xmmap_file(int fd, struct stat *st);

would probably work. We could even do the fstat() on behalf of the caller, though they need to know the length themselves. Maybe:

  void *xmmap_file(int fd, size_t *len);

I dunno if it is worth it or not.

 config.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/config.c b/config.c
index e7dc155..29fa012 100644
--- a/config.c
+++ b/config.c
@@ -2056,6 +2056,8 @@ int git_config_set_multivar_in_file(const char *config_filename,
 		contents = xmmap_gently(NULL, contents_sz, PROT_READ,
 					MAP_PRIVATE, in_fd, 0);
 		if (contents == MAP_FAILED) {
+			if (errno == ENODEV && S_ISDIR(st.st_mode))
+				errno = EISDIR;
 			error("unable to mmap '%s': %s",
 			      config_filename, strerror(errno));
 			ret = CONFIG_INVALID_FILE;

-- 
2.4.2.668.gc3b1ade.dirty