Re: Versioning configuration files on a server: fatal: Unable to create '//etc/.git/index.lock': No such file or directory

From: Matthijs Kooijman <matthijs@stdin.nl>
Date: Nov 18, 2010, 20:36 UTC
Message-ID: <20101118203617.GH22067@login.drsnuggles.stderr.nl>
In-Reply-To: <20101118171751.GG22067@login.drsnuggles.stderr.nl>

Hi folks,

Show 5 quoted lines

> > I think 490544b (get_cwd_relative(): do not misinterpret suffix as
> > subdirectory - 2010-05-22) causes it. Haven't fully understood what's
> > going on in that function though :P
> Seems you're right. I just reverted this commit and the problem seems to
> go away.

A bit more gdb'ing with -O0, I found the following. get_cwd_relative is called with dir="/". The cwd is "/etc". The stack looks like:

#0 get_relative_cwd (buffer=0x7a44c0 "/etc", size=4096, dir=0x7b1041 "") at dir.c:961 #1 0x00000000004dfdf1 in setup_git_directory () at setup.c:612 #2 0x0000000000404f69 in run_builtin (p=0x75ea10, argc=2, argv=0x7fffffffc918) at git.c:257 #3 0x00000000004051e3 in handle_internal_command (argc=2, argv=0x7fffffffc918) at git.c:431 #4 0x000000000040538a in main (argc=2, argv=0x7fffffffc918) at git.c:516

After the following code runs:

    while (*dir && *dir == *cwd) {
	    dir++; 
	    cwd++;
    }

I have dir="" and cwd="etc". Then the following code runs:

    switch (*cwd) {
    case '\0':
	    return cwd;
    case '/':
	    return cwd + 1;
    default:
	    return NULL;
    }

Since *cwd='e', it returns NULL.

The old code (before 490544b) was:

   if (*cwd == '/')
	   return cwd + 1;
   return cwd;

So this would return "etc".

So, that's what is happens. I think this happens because get_relative_cwd expects dir to not contain a trailing slash. Normally, there is no trailing slash, but in the special case of dir="/" there is (sort of) a trailing slash.

I'm not completely sure how to fix this. Looking at 72ec8ba (Support working directory located at root - 2010-02-14), perhaps something like this?

diff --git a/dir.c b/dir.c
index d1e5e5e..5408db9 100644
--- a/dir.c
+++ b/dir.c
@@ -943,6 +943,7 @@ int file_exists(const char *f)
 char *get_relative_cwd(char *buffer, int size, const char *dir)
 {
        char *cwd = buffer;
+       size_t len, root_len;
 
        if (!dir)
                return NULL;
@@ -952,6 +953,15 @@ char *get_relative_cwd(char *buffer, int size, const char *dir)
        if (!is_absolute_path(dir))
                dir = make_absolute_path(dir);
 
+       len = strlen(dir);
+       root_len = offset_1st_component(dir);
+
+       if (root_len >= len) {
+           /* dir is the filesystem root, so the cwd is always inside */
+           root_len = offset_1st_component(cwd);
+           return cwd + root_len;
+       }
+
        while (*dir && *dir == *cwd) {
                dir++;
                cwd++;

I'm not sure how this stuff really works, though. I think this works for *nix,
but I'm unsure about Windows.

Gr.

Matthijs