Re: [RFC PATCHv6 1/2] repack: rewrite the shell script in C

Stefan Beller [off-list ref] writes:

The motivation of this patch is to get closer to a goal of being
able to have a core subset of git functionality built in to git.
That would mean

 * people on Windows could get a copy of at least the core parts
   of Git without having to install a Unix-style shell

 * people deploying to servers don't have to rewrite the #! line
   or worry about the PATH and quality of installed POSIX
   utilities, if they are only using the built-in part written
   in C

I am not sure what is meant by the latter.  Rewriting #! is part of
any scripted Porcelain done by the top-level Makefile, and I do not
think we have seen any problem reports on it.

As to "quality of ... utilities", I think the real issue some people
in the thread had was not about "deploying to servers" but about
installing in a minimalistic chrooted environment where standard
tools may be lacking.

I am not sure if we want to record "ownership" in the code like
this; it will go stale over time.

+#include "builtin.h"
+#include "cache.h"
+#include "dir.h"
+#include "parse-options.h"
+#include "run-command.h"
+#include "sigchain.h"
+#include "strbuf.h"
+#include "string-list.h"
+#include "argv-array.h"
+
+/* enabled by default since 22c79eab (2008-06-25) */

It may be of some value that by default --delta-base-offset is used,
but that can be read from the initialization.  Do we need this
comment?

+static int delta_base_offset = 1;
+char *packdir;

Does this have to be global?

+static const char *const git_repack_usage[] = {
+	N_("git repack [options]"),
+	NULL
+};
+
+static int repack_config(const char *var, const char *value, void *cb)
+{
+	if (!strcmp(var, "repack.usedeltabaseoffset")) {
+		delta_base_offset = git_config_bool(var, value);
+		return 0;
+	}
+	return git_default_config(var, value, cb);
+}
+
+/*
+ * Remove temporary $GIT_OBJECT_DIRECTORY/pack/.tmp-$$-pack-* files.
+ */
+static void remove_temporary_files(void)
+{
+	struct strbuf buf = STRBUF_INIT;
+	size_t dirlen, prefixlen;
+	DIR *dir;
+	struct dirent *e;
+
+	/* .git/objects/pack */

We can read what is in there from two strbuf calls without comment.

+	strbuf_addstr(&buf, get_object_directory());
+	strbuf_addstr(&buf, "/pack");

More importantly, you already know what this directory and what
packtmp prefix are.

Also, you can keep &buf empty until opendir() succeeds.

+	dir = opendir(buf.buf);
+	if (!dir) {
+		strbuf_release(&buf);
+		return;
+	}
+
+	/* .git/objects/pack/.tmp-$$-pack-* */
+	dirlen = buf.len + 1;

Likewise; it is a good idea to document what "dirlen" points at,
though.

+	strbuf_addf(&buf, "/.tmp-%d-pack-", (int)getpid());
+	prefixlen = buf.len - dirlen;

So in summary:

	dir = opendir(packdir);
        if (!dir)
		return;

	strbuf_addf(&buf, "%s-", packtmp);

        /* Point at the slash at the end of ".../objects/pack/" */
	dirlen = strlen(packdir) + 1;
        /* Point at the dash at the end of ".../.tmp-%d-pack-" */
        prefixlen = buf.len - dirlen;

You would need to move the initialization of packdir and packtmp
before sigchain_push() in cmd_repack() if you were to do this.

+	while ((e = readdir(dir))) {
+		if (strncmp(e->d_name, buf.buf + dirlen, prefixlen))
+			continue;
+		strbuf_setlen(&buf, dirlen);
+		strbuf_addstr(&buf, e->d_name);
+		unlink(buf.buf);

This unlink(2) could fail, but there is not much we could do here.

+	}
+	closedir(dir);
+	strbuf_release(&buf);
+}
+
+static void remove_pack_on_signal(int signo)
+{
+	remove_temporary_files();
+	sigchain_pop(signo);
+	raise(signo);
+}
+
+static void get_pack_filenames(struct string_list *fname_list)
+{
+	DIR *dir;
+	struct dirent *e;
+	char *fname;
+
+	if (!(dir = opendir(packdir)))
+		return;
+
+	while ((e = readdir(dir)) != NULL) {
+		if (suffixcmp(e->d_name, ".pack"))
+			continue;

We may want to tighten this to ignore cruft that does not match

	/^pack-[0-9a-f]{40}\.pack$/

in a later patch, but this is a faithful rewrite from the original.

+		size_t len = strlen(e->d_name) - strlen(".pack");

decl-after-stmt.

+		fname = xmemdupz(e->d_name, len);
+
+		if (!file_exists(mkpath("%s/%s.keep", packdir, fname)))
+			string_list_append_nodup(fname_list, fname);

mental note: this is getting names of non-kept packs, not all packs.

+	}
+	closedir(dir);
+}
+
+static void remove_redundant_pack(const char *path, const char *sha1)

These parameter names may want to be changed to clarify what they
are; see below.

+{
+	const char *exts[] = {".pack", ".idx", ".keep"};
+	int i;
+	struct strbuf buf = STRBUF_INIT;
+	size_t plen;
+
+	strbuf_addf(&buf, "%s/%s", path, sha1);

This suggests that path[] has ".../objects/pack/pack-" and sha1[] is
a 40-hex representation of the pack name.  Calling the former
path_prefix[] and the latter hex[] may be clearer.

+	plen = buf.len;
+
+	for (i = 0; i < ARRAY_SIZE(exts); i++) {
+		strbuf_setlen(&buf, plen);
+		strbuf_addstr(&buf, exts[i]);
+		unlink(buf.buf);
+	}
+}
+
+int cmd_repack(int argc, const char **argv, const char *prefix)
+{
+	const char *exts[2] = {".idx", ".pack"};
+	char *packtmp;
+	struct child_process cmd;
+	struct string_list_item *item;
+	struct argv_array cmd_args = ARGV_ARRAY_INIT;
+	struct string_list names = STRING_LIST_INIT_DUP;
+	struct string_list rollback = STRING_LIST_INIT_DUP;
+	struct string_list existing_packs = STRING_LIST_INIT_DUP;
+	struct strbuf line = STRBUF_INIT;
+	int count_packs, ext, ret;
+	FILE *out;
+
+	/* variables to be filled by option parsing */
+	int pack_everything = 0;
+	int pack_everything_but_loose = 0;
+	int delete_redundant = 0;
+	char *unpack_unreachable = NULL;
+	int window = 0, window_memory = 0;
+	int depth = 0;
+	int max_pack_size = 0;
+	int no_reuse_delta = 0, no_reuse_object = 0;
+	int no_update_server_info = 0;
+	int quiet = 0;
+	int local = 0;
+
+	struct option builtin_repack_options[] = {
+		OPT_BOOL('a', NULL, &pack_everything,
+				N_("pack everything in a single pack")),
+		OPT_BOOL('A', NULL, &pack_everything_but_loose,
+				N_("same as -a, and turn unreachable objects loose")),
+		OPT_BOOL('d', NULL, &delete_redundant,
+				N_("remove redundant packs, and run git-prune-packed")),
+		OPT_BOOL('f', NULL, &no_reuse_delta,
+				N_("pass --no-reuse-delta to git-pack-objects")),
+		OPT_BOOL('F', NULL, &no_reuse_object,
+				N_("pass --no-reuse-object to git-pack-objects")),
+		OPT_BOOL('n', NULL, &no_update_server_info,
+				N_("do not run git-update-server-info")),
+		OPT__QUIET(&quiet, N_("be quiet")),
+		OPT_BOOL('l', "local", &local,
+				N_("pass --local to git-pack-objects")),
+		OPT_STRING(0, "unpack-unreachable", &unpack_unreachable, N_("approxidate"),
+				N_("with -A, do not loosen objects older than this")),
+		OPT_INTEGER(0, "window", &window,
+				N_("size of the window used for delta compression")),
+		OPT_INTEGER(0, "window-memory", &window_memory,
+				N_("same as the above, but limit memory size instead of entries count")),
+		OPT_INTEGER(0, "depth", &depth,
+				N_("limits the maximum delta depth")),
+		OPT_INTEGER(0, "max-pack-size", &max_pack_size,
+				N_("maximum size of each packfile")),
+		OPT_END()
+	};
+
+	git_config(repack_config, NULL);
+
+	argc = parse_options(argc, argv, prefix, builtin_repack_options,
+				git_repack_usage, 0);

Nice. In a later patch we might want to allow --delta-base-offset to
be overridden from the command line and doing config first and then
options second like the above would allow us to do so easily.

+	sigchain_push_common(remove_pack_on_signal);
+	packdir = mkpathdup("%s/pack", get_object_directory());
+	packtmp = mkpathdup("%s/.tmp-%d-pack", packdir, (int)getpid());
+
+	argv_array_push(&cmd_args, "pack-objects");
+	argv_array_push(&cmd_args, "--keep-true-parents");
+	argv_array_push(&cmd_args, "--honor-pack-keep");
+	argv_array_push(&cmd_args, "--non-empty");
+	argv_array_push(&cmd_args, "--all");
+	argv_array_push(&cmd_args, "--reflog");
+	if (window)
+		argv_array_pushf(&cmd_args, "--window=%u", window);
+	if (window_memory)
+		argv_array_pushf(&cmd_args, "--window-memory=%u", window_memory);
+	if (depth)
+		argv_array_pushf(&cmd_args, "--depth=%u", depth);
+	if (max_pack_size)
+		argv_array_pushf(&cmd_args, "--max_pack_size=%u", max_pack_size);
+	if (no_reuse_delta)
+		argv_array_pushf(&cmd_args, "--no-reuse-delta");
+	if (no_reuse_object)
+		argv_array_pushf(&cmd_args, "--no-reuse-object");
+
+	if (!pack_everything && !pack_everything_but_loose) {
+		argv_array_push(&cmd_args, "--unpacked");
+		argv_array_push(&cmd_args, "--incremental");
+	} else {
+		get_pack_filenames(&existing_packs);
+
+		if (existing_packs.nr && delete_redundant) {
+			if (unpack_unreachable)
+				argv_array_pushf(&cmd_args,
+						"--unpack-unreachable=%s",
+						unpack_unreachable);
+			else if (pack_everything_but_loose)
+				argv_array_push(&cmd_args,
+						"--unpack-unreachable");
+		}
+	}
+
+	if (local)
+		argv_array_push(&cmd_args,  "--local");
+	if (quiet)
+		argv_array_push(&cmd_args,  "--quiet");

The original seems to push "-q", but it is probably OK to make it
more readable by spelling it out like this.

+	if (delta_base_offset)
+		argv_array_push(&cmd_args,  "--delta-base-offset");
+
+	argv_array_push(&cmd_args, packtmp);
+
+	memset(&cmd, 0, sizeof(cmd));
+	cmd.argv = cmd_args.argv;
+	cmd.git_cmd = 1;
+	cmd.out = -1;
+	cmd.no_stdin = 1;
+
+	ret = start_command(&cmd);
+	if (ret)
+		return 1;
+
+	count_packs = 0;
+	out = xfdopen(cmd.out, "r");
+	while (strbuf_getline(&line, out, '\n') != EOF) {
+		if (line.len != 40)
+			die("repack: Expecting 40 character sha1 lines only from pack-objects.");
+		strbuf_addstr(&line, "");

What is this addstr() about?

+		string_list_append(&names, line.buf);
+		count_packs++;

It probably is more in line with our naming convention to call this
nr_packs, num_packs, etc.  "count_packs" sounds more like a boolean
that instructs the code to either count or not bother counting,
which this thing is not.

+	}
+	fclose(out);
+	ret = finish_command(&cmd);
+	if (ret)
+		return 1;
+	argv_array_clear(&cmd_args);
+
+	if (!count_packs && !quiet)
+		printf("Nothing new to pack.\n");
+
+	int failed = 0;

decl-after-stmt.

+	for_each_string_list_item(item, &names) {
+		for (ext = 0; ext < 2; ext++) {
+			char *fname, *fname_old;
+			fname = mkpathdup("%s/%s%s", packdir,
+						item->string, exts[ext]);
+			if (!file_exists(fname)) {
+				free(fname);
+				continue;
+			}
+
+			fname_old = mkpathdup("%s/old-%s%s", packdir,
+						item->string, exts[ext]);
+			if (file_exists(fname_old))
+				unlink(fname_old);
+
+			if (rename(fname, fname_old)) {
+				failed = 1;
+				break;

"break"-ing from here leaks fname_old.  As the only out-of-line call
file_exists() is just a thin wrapper around lstat(), I think it is
fine not to pathdup the fname_old here.

+			}
+			string_list_append_nodup(&rollback, fname);
+			free(fname);

This looks bad, doesn't it?  append_nodup() lets &rollback string
list to take the ownership of the piece of memory pointed at by
fname, but then you free it here, no?

If you initialize &rollback with INIT_NODUP, you would not have to
call append_nodup().

+			free(fname_old);
+		}
+		if (failed)
+			break;
+	}
+	if (failed) {
+		struct string_list rollback_failure;

Initialization?

+		for_each_string_list_item(item, &rollback) {
+			char *fname, *fname_old;
+			fname = mkpathdup("%s/%s", packdir, item->string);
+			fname_old = mkpath("%s/old-%s", packdir, item->string);
+			if (rename(fname_old, fname))
+				string_list_append(&rollback_failure, fname);
+			free(fname);
+		}