tmp-objdir: introduce API for temporary object directories

[thirdparty/git.git] / tmp-objdir.c

#include "cache.h"
#include "tmp-objdir.h"
#include "dir.h"
#include "sigchain.h"
#include "string-list.h"
#include "strbuf.h"
#include "argv-array.h"

struct tmp_objdir {
	struct strbuf path;
	struct argv_array env;
};

/*
 * Allow only one tmp_objdir at a time in a running process, which simplifies
 * our signal/atexit cleanup routines.  It's doubtful callers will ever need
 * more than one, and we can expand later if so.  You can have many such
 * tmp_objdirs simultaneously in many processes, of course.
 */
static struct tmp_objdir *the_tmp_objdir;

static void tmp_objdir_free(struct tmp_objdir *t)
{
	strbuf_release(&t->path);
	argv_array_clear(&t->env);
	free(t);
}

static int tmp_objdir_destroy_1(struct tmp_objdir *t, int on_signal)
{
	int err;

	if (!t)
		return 0;

	if (t == the_tmp_objdir)
		the_tmp_objdir = NULL;

	/*
	 * This may use malloc via strbuf_grow(), but we should
	 * have pre-grown t->path sufficiently so that this
	 * doesn't happen in practice.
	 */
	err = remove_dir_recursively(&t->path, 0);

	/*
	 * When we are cleaning up due to a signal, we won't bother
	 * freeing memory; it may cause a deadlock if the signal
	 * arrived while libc's allocator lock is held.
	 */
	if (!on_signal)
		tmp_objdir_free(t);
	return err;
}

int tmp_objdir_destroy(struct tmp_objdir *t)
{
	return tmp_objdir_destroy_1(t, 0);
}

static void remove_tmp_objdir(void)
{
	tmp_objdir_destroy(the_tmp_objdir);
}

static void remove_tmp_objdir_on_signal(int signo)
{
	tmp_objdir_destroy_1(the_tmp_objdir, 1);
	sigchain_pop(signo);
	raise(signo);
}

/*
 * These env_* functions are for setting up the child environment; the
 * "replace" variant overrides the value of any existing variable with that
 * "key". The "append" variant puts our new value at the end of a list,
 * separated by PATH_SEP (which is what separate values in
 * GIT_ALTERNATE_OBJECT_DIRECTORIES).
 */
static void env_append(struct argv_array *env, const char *key, const char *val)
{
	const char *old = getenv(key);

	if (!old)
		argv_array_pushf(env, "%s=%s", key, val);
	else
		argv_array_pushf(env, "%s=%s%c%s", key, old, PATH_SEP, val);
}

static void env_replace(struct argv_array *env, const char *key, const char *val)
{
	argv_array_pushf(env, "%s=%s", key, val);
}

static int setup_tmp_objdir(const char *root)
{
	char *path;
	int ret = 0;

	path = xstrfmt("%s/pack", root);
	ret = mkdir(path, 0777);
	free(path);

	return ret;
}

struct tmp_objdir *tmp_objdir_create(void)
{
	static int installed_handlers;
	struct tmp_objdir *t;

	if (the_tmp_objdir)
		die("BUG: only one tmp_objdir can be used at a time");

	t = xmalloc(sizeof(*t));
	strbuf_init(&t->path, 0);
	argv_array_init(&t->env);

	strbuf_addf(&t->path, "%s/incoming-XXXXXX", get_object_directory());

	/*
	 * Grow the strbuf beyond any filename we expect to be placed in it.
	 * If tmp_objdir_destroy() is called by a signal handler, then
	 * we should be able to use the strbuf to remove files without
	 * having to call malloc.
	 */
	strbuf_grow(&t->path, 1024);

	if (!mkdtemp(t->path.buf)) {
		/* free, not destroy, as we never touched the filesystem */
		tmp_objdir_free(t);
		return NULL;
	}

	the_tmp_objdir = t;
	if (!installed_handlers) {
		atexit(remove_tmp_objdir);
		sigchain_push_common(remove_tmp_objdir_on_signal);
		installed_handlers++;
	}

	if (setup_tmp_objdir(t->path.buf)) {
		tmp_objdir_destroy(t);
		return NULL;
	}

	env_append(&t->env, ALTERNATE_DB_ENVIRONMENT,
		   absolute_path(get_object_directory()));
	env_replace(&t->env, DB_ENVIRONMENT, absolute_path(t->path.buf));

	return t;
}

/*
 * Make sure we copy packfiles and their associated metafiles in the correct
 * order. All of these ends_with checks are slightly expensive to do in
 * the midst of a sorting routine, but in practice it shouldn't matter.
 * We will have a relatively small number of packfiles to order, and loose
 * objects exit early in the first line.
 */
static int pack_copy_priority(const char *name)
{
	if (!starts_with(name, "pack"))
		return 0;
	if (ends_with(name, ".keep"))
		return 1;
	if (ends_with(name, ".pack"))
		return 2;
	if (ends_with(name, ".idx"))
		return 3;
	return 4;
}

static int pack_copy_cmp(const char *a, const char *b)
{
	return pack_copy_priority(a) - pack_copy_priority(b);
}

static int read_dir_paths(struct string_list *out, const char *path)
{
	DIR *dh;
	struct dirent *de;

	dh = opendir(path);
	if (!dh)
		return -1;

	while ((de = readdir(dh)))
		if (!is_dot_or_dotdot(de->d_name))
			string_list_append(out, de->d_name);

	closedir(dh);
	return 0;
}

static int migrate_paths(struct strbuf *src, struct strbuf *dst);

static int migrate_one(struct strbuf *src, struct strbuf *dst)
{
	struct stat st;

	if (stat(src->buf, &st) < 0)
		return -1;
	if (S_ISDIR(st.st_mode)) {
		if (!mkdir(dst->buf, 0777)) {
			if (adjust_shared_perm(dst->buf))
				return -1;
		} else if (errno != EEXIST)
			return -1;
		return migrate_paths(src, dst);
	}
	return finalize_object_file(src->buf, dst->buf);
}

static int migrate_paths(struct strbuf *src, struct strbuf *dst)
{
	size_t src_len = src->len, dst_len = dst->len;
	struct string_list paths = STRING_LIST_INIT_DUP;
	int i;
	int ret = 0;

	if (read_dir_paths(&paths, src->buf) < 0)
		return -1;
	paths.cmp = pack_copy_cmp;
	string_list_sort(&paths);

	for (i = 0; i < paths.nr; i++) {
		const char *name = paths.items[i].string;

		strbuf_addf(src, "/%s", name);
		strbuf_addf(dst, "/%s", name);

		ret |= migrate_one(src, dst);

		strbuf_setlen(src, src_len);
		strbuf_setlen(dst, dst_len);
	}

	string_list_clear(&paths, 0);
	return ret;
}

int tmp_objdir_migrate(struct tmp_objdir *t)
{
	struct strbuf src = STRBUF_INIT, dst = STRBUF_INIT;
	int ret;

	if (!t)
		return 0;

	strbuf_addbuf(&src, &t->path);
	strbuf_addstr(&dst, get_object_directory());

	ret = migrate_paths(&src, &dst);

	strbuf_release(&src);
	strbuf_release(&dst);

	tmp_objdir_destroy(t);
	return ret;
}

const char **tmp_objdir_env(const struct tmp_objdir *t)
{
	if (!t)
		return NULL;
	return t->env.argv;
}

void tmp_objdir_add_as_alternate(const struct tmp_objdir *t)
{
	add_to_alternates_memory(t->path.buf);
}