Re: Creating objects manually and repack

From: Linus Torvalds <torvalds@osdl.org>
Date: Aug 4, 2006, 18:06 UTC
Message-ID: <Pine.LNX.4.64.0608041052030.5167@g5.osdl.org>
In-Reply-To: <Pine.LNX.4.64.0608041027530.5167@g5.osdl.org>

On Fri, 4 Aug 2006, Linus Torvalds wrote:

Show 6 quoted lines

> 
> You may definitely want to pack the pack-files together every once in a 
> while. Doing so is not that hard: just list all the objects in all the 
> pack-files you want to merge, which in turn is trivial from reading the 
> index of the pack-files (and then you do want to do the filename, 
> although you can just use the pack-file name if you want to).

Btw, that index format is actually documented (and it really is _very_ simple) in Documentation/technical/pack-format.txt.

To get a list of all object names in a pack-file, you'd basically do just something like the appended. So with this (let's call it "git-list-objects"), you could just do

	for i in $packlist
	do
		git-list-objects $i.idx
	done | git-pack-objects combined-pack

and it would combine all the packs in "$packlist" into one new "combined-pack-<sha1>" pack.

And no, I didn't actually _test_ any of this, but it looks pretty damn simple.

		Linus

---- #include <unistd.h> #include <fcntl.h> #include <stdio.h>

#define CHUNK (100)

int main(int argc, char **argv)
{
	static unsigned char buffer[24*CHUNK];
	const char *name = argv[1];
	unsigned int n;
	int fd;
	int i;

	if (!name)
		die("no filename!");

	fd = open(name, O_RDONLY);
	if (fd < 0)
		perror(name);

	/* throw away the first-level fan-out */
	if (read(fd, buffer, 4*256) != 4*256)
		perror("read fan-out");

	n = (buffer[4*255 + 0] << 24) +
	    (buffer[4*255 + 1] << 16) +
	    (buffer[4*255 + 2] << 8) +
	    (buffer[4*255 + 3] << 0);

	for (i = 0; i < n; i += CHUNK) {
		int j, left = n - i;
		if (left > CHUNK)
			left = CHUNK;
		if (read(fd, buffer, left*24) != left*24)
			perror("read chunk");
		for (j = 0; j < left; j++) {
			const unsigned char *sha1;
			sha1 = buffer + j*24 + 4;
			printf("%s %s\n", sha1_to_hex(sha1), name);
		}
	}
	return 0;
}