Re: git and symlinks as tracked content

From: Linus Torvalds <torvalds@osdl.org>
Date: May 3, 2005, 19:02 UTC
Message-ID: <Pine.LNX.4.58.0505031151240.26698@ppc970.osdl.org>
In-Reply-To: <1115145234.21105.111.camel@localhost.localdomain>

On Tue, 3 May 2005, Kay Sievers wrote:

Show 7 quoted lines

>
> Is there a sane model to make git aware of tracking symlinks in the
> repository? In the bk udev tree we've had a test sysfs-tree with a lot
> of symlinks in it.
> 
> Where can we store the link-target? In its own blob-object or directly
> in the tree-object?

I'd suggest you create a blob object with the symlink name, and then in the tree you point to that blob, but with the S_IFLNK value in the mode field (0120000).

So you have

 - directories: S_IFDIR (0040000) point to "tree" objects for contents
 - symlinks: S_IFLNK (0120000) point to "blob" objects
 - executables: S_IFREG | 0755 (0100755) point to "blob" objects
 - regular files: S_IFREG | 0644 (0100644) point to "blob" objects

which seems very sane and regular.

Now, I also haev a plan for device nodes, but that one is so ugly that I'm a bit ashamed of it. That one does:

 - S_IFCHR/S_IFBLK (0020000 or 0060000), with the 20-byte SHA1 not being a 
   SHA1 at all, but just the major:minor numbers in some nice binary 
   encoding. Probably: two network byte order 32-bit values, with twelve 
   bytes of some non-zero signature (the SHA1 of all zeroes should be 
   avoided, so the signature really should be soemthing else than just 
   twelve bytes of zero).

That should cover most of it.

> How would a exported "patch" with symlinks as content look like?

The easiest way is to make this exactly the same as the "executable bit". A symlink is just a normal blob, it just has a "symlink mode" instead of "0755" or "0644" mode.

When you think of it that way, the "patch" ends up falling out very naturally, I think. It would look like

	New file: filename (Mode: 0120000)
	--- /dev/null
	+++ filename
	@@ 0,0 1,1
	+symlink-value

(or something, you get the idea).

		Linus