Merge branch 'ew/mmap-failures'

Error message update.

* ew/mmap-failures:
  xmmap: inform Linux users of tuning knobs on ENOMEM

config.c

@@ -3052,7 +3052,8 @@ int git_config_set_multivar_in_file_gently(const char *config_filename,
 		if (contents == MAP_FAILED) {
 			if (errno == ENODEV && S_ISDIR(st.st_mode))
 				errno = EISDIR;
-			error_errno(_("unable to mmap '%s'"), config_filename);
+			error_errno(_("unable to mmap '%s'%s"),
+					config_filename, mmap_os_err());
 			ret = CONFIG_INVALID_FILE;
 			contents = NULL;
 			goto out_free;

git-compat-util.h

@@ -876,6 +876,7 @@ char *xstrndup(const char *str, size_t len);
 void *xrealloc(void *ptr, size_t size);
 void *xcalloc(size_t nmemb, size_t size);
 void *xmmap(void *start, size_t length, int prot, int flags, int fd, off_t offset);
+const char *mmap_os_err(void);
 void *xmmap_gently(void *start, size_t length, int prot, int flags, int fd, off_t offset);
 int xopen(const char *path, int flags, ...);
 ssize_t xread(int fd, void *buf, size_t len);

object-file.c

@@ -1023,12 +1023,26 @@ void *xmmap_gently(void *start, size_t length,
 	return ret;
 }
 
+const char *mmap_os_err(void)
+{
+	static const char blank[] = "";
+#if defined(__linux__)
+	if (errno == ENOMEM) {
+		/* this continues an existing error message: */
+		static const char enomem[] =
+", check sys.vm.max_map_count and/or RLIMIT_DATA";
+		return enomem;
+	}
+#endif /* OS-specific bits */
+	return blank;
+}
+
 void *xmmap(void *start, size_t length,
 	int prot, int flags, int fd, off_t offset)
 {
 	void *ret = xmmap_gently(start, length, prot, flags, fd, offset);
 	if (ret == MAP_FAILED)
-		die_errno(_("mmap failed"));
+		die_errno(_("mmap failed%s"), mmap_os_err());
 	return ret;
 }
 

packfile.c

@@ -652,8 +652,8 @@ unsigned char *use_pack(struct packed_git *p,
 				PROT_READ, MAP_PRIVATE,
 				p->pack_fd, win->offset);
 			if (win->base == MAP_FAILED)
-				die_errno("packfile %s cannot be mapped",
-					  p->pack_name);
+				die_errno(_("packfile %s cannot be mapped%s"),
+					  p->pack_name, mmap_os_err());
 			if (!win->offset && win->len == p->pack_size
 				&& !p->do_not_close)
 				close_pack_fd(p);

read-cache.c

@@ -2233,7 +2233,8 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 
 	mmap = xmmap_gently(NULL, mmap_size, PROT_READ, MAP_PRIVATE, fd, 0);
 	if (mmap == MAP_FAILED)
-		die_errno(_("%s: unable to map index file"), path);
+		die_errno(_("%s: unable to map index file%s"), path,
+			mmap_os_err());
 	close(fd);
 
 	hdr = (const struct cache_header *)mmap;