git/bulk-checkin.c

/*
 * Copyright (c) 2011, Google Inc.
 */
#include "cache.h"
#include "bulk-checkin.h"
#include "lockfile.h"
#include "repository.h"
#include "csum-file.h"
#include "pack.h"
#include "strbuf.h"
#include "string-list.h"
#include "tmp-objdir.h"
#include "packfile.h"
#include "object-store.h"

static int odb_transaction_nesting;

static struct tmp_objdir *bulk_fsync_objdir;

static struct bulk_checkin_packfile {
	char *pack_tmp_name;
	struct hashfile *f;
	off_t offset;
	struct pack_idx_option pack_idx_opts;

	struct pack_idx_entry **written;
	uint32_t alloc_written;
	uint32_t nr_written;
} bulk_checkin_packfile;

static void finish_tmp_packfile(struct strbuf *basename,
				const char *pack_tmp_name,
				struct pack_idx_entry **written_list,
				uint32_t nr_written,
				struct pack_idx_option *pack_idx_opts,
				unsigned char hash[])
{
	char *idx_tmp_name = NULL;

	stage_tmp_packfiles(basename, pack_tmp_name, written_list, nr_written,
			    NULL, pack_idx_opts, hash, &idx_tmp_name);
	rename_tmp_packfile_idx(basename, &idx_tmp_name);

	free(idx_tmp_name);
}

static void flush_bulk_checkin_packfile(struct bulk_checkin_packfile *state)
{
	unsigned char hash[GIT_MAX_RAWSZ];
	struct strbuf packname = STRBUF_INIT;
	int i;

	if (!state->f)
		return;

	if (state->nr_written == 0) {
		close(state->f->fd);
		unlink(state->pack_tmp_name);
		goto clear_exit;
	} else if (state->nr_written == 1) {
		finalize_hashfile(state->f, hash, FSYNC_COMPONENT_PACK,
				  CSUM_HASH_IN_STREAM | CSUM_FSYNC | CSUM_CLOSE);
	} else {
		int fd = finalize_hashfile(state->f, hash, FSYNC_COMPONENT_PACK, 0);
		fixup_pack_header_footer(fd, hash, state->pack_tmp_name,
					 state->nr_written, hash,
					 state->offset);
		close(fd);
	}

	strbuf_addf(&packname, "%s/pack/pack-%s.", get_object_directory(),
		    hash_to_hex(hash));
	finish_tmp_packfile(&packname, state->pack_tmp_name,
			    state->written, state->nr_written,
			    &state->pack_idx_opts, hash);
	for (i = 0; i < state->nr_written; i++)
		free(state->written[i]);

clear_exit:
	free(state->written);
	memset(state, 0, sizeof(*state));

	strbuf_release(&packname);
	/* Make objects we just wrote available to ourselves */
	reprepare_packed_git(the_repository);
}

/*
 * Cleanup after batch-mode fsync_object_files.
 */
static void flush_batch_fsync(void)
{
	struct strbuf temp_path = STRBUF_INIT;
	struct tempfile *temp;

	if (!bulk_fsync_objdir)
		return;

	/*
	 * Issue a full hardware flush against a temporary file to ensure
	 * that all objects are durable before any renames occur. The code in
	 * fsync_loose_object_bulk_checkin has already issued a writeout
	 * request, but it has not flushed any writeback cache in the storage
	 * hardware or any filesystem logs. This fsync call acts as a barrier
	 * to ensure that the data in each new object file is durable before
	 * the final name is visible.
	 */
	strbuf_addf(&temp_path, "%s/bulk_fsync_XXXXXX", get_object_directory());
	temp = xmks_tempfile(temp_path.buf);
	fsync_or_die(get_tempfile_fd(temp), get_tempfile_path(temp));
	delete_tempfile(&temp);
	strbuf_release(&temp_path);

	/*
	 * Make the object files visible in the primary ODB after their data is
	 * fully durable.
	 */
	tmp_objdir_migrate(bulk_fsync_objdir);
	bulk_fsync_objdir = NULL;
}

static int already_written(struct bulk_checkin_packfile *state, struct object_id *oid)
{
	int i;

	/* The object may already exist in the repository */
	if (has_object_file(oid))
		return 1;

	/* Might want to keep the list sorted */
	for (i = 0; i < state->nr_written; i++)
		if (oideq(&state->written[i]->oid, oid))
			return 1;

	/* This is a new object we need to keep */
	return 0;
}

/*
 * Read the contents from fd for size bytes, streaming it to the
 * packfile in state while updating the hash in ctx. Signal a failure
 * by returning a negative value when the resulting pack would exceed
 * the pack size limit and this is not the first object in the pack,
 * so that the caller can discard what we wrote from the current pack
 * by truncating it and opening a new one. The caller will then call
 * us again after rewinding the input fd.
 *
 * The already_hashed_to pointer is kept untouched by the caller to
 * make sure we do not hash the same byte when we are called
 * again. This way, the caller does not have to checkpoint its hash
 * status before calling us just in case we ask it to call us again
 * with a new pack.
 */
static int stream_to_pack(struct bulk_checkin_packfile *state,
			  git_hash_ctx *ctx, off_t *already_hashed_to,
			  int fd, size_t size, enum object_type type,
			  const char *path, unsigned flags)
{
	git_zstream s;
	unsigned char ibuf[16384];
	unsigned char obuf[16384];
	unsigned hdrlen;
	int status = Z_OK;
	int write_object = (flags & HASH_WRITE_OBJECT);
	off_t offset = 0;

	git_deflate_init(&s, pack_compression_level);

	hdrlen = encode_in_pack_object_header(obuf, sizeof(obuf), type, size);
	s.next_out = obuf + hdrlen;
	s.avail_out = sizeof(obuf) - hdrlen;

	while (status != Z_STREAM_END) {
		if (size && !s.avail_in) {
			ssize_t rsize = size < sizeof(ibuf) ? size : sizeof(ibuf);
			ssize_t read_result = read_in_full(fd, ibuf, rsize);
			if (read_result < 0)
				die_errno("failed to read from '%s'", path);
			if (read_result != rsize)
				die("failed to read %d bytes from '%s'",
				    (int)rsize, path);
			offset += rsize;
			if (*already_hashed_to < offset) {
				size_t hsize = offset - *already_hashed_to;
				if (rsize < hsize)
					hsize = rsize;
				if (hsize)
					the_hash_algo->update_fn(ctx, ibuf, hsize);
				*already_hashed_to = offset;
			}
			s.next_in = ibuf;
			s.avail_in = rsize;
			size -= rsize;
		}

		status = git_deflate(&s, size ? 0 : Z_FINISH);

		if (!s.avail_out || status == Z_STREAM_END) {
			if (write_object) {
				size_t written = s.next_out - obuf;

				/* would we bust the size limit? */
				if (state->nr_written &&
				    pack_size_limit_cfg &&
				    pack_size_limit_cfg < state->offset + written) {
					git_deflate_abort(&s);
					return -1;
				}

				hashwrite(state->f, obuf, written);
				state->offset += written;
			}
			s.next_out = obuf;
			s.avail_out = sizeof(obuf);
		}

		switch (status) {
		case Z_OK:
		case Z_BUF_ERROR:
		case Z_STREAM_END:
			continue;
		default:
			die("unexpected deflate failure: %d", status);
		}
	}
	git_deflate_end(&s);
	return 0;
}

/* Lazily create backing packfile for the state */
static void prepare_to_stream(struct bulk_checkin_packfile *state,
			      unsigned flags)
{
	if (!(flags & HASH_WRITE_OBJECT) || state->f)
		return;

	state->f = create_tmp_packfile(&state->pack_tmp_name);
	reset_pack_idx_option(&state->pack_idx_opts);

	/* Pretend we are going to write only one object */
	state->offset = write_pack_header(state->f, 1);
	if (!state->offset)
		die_errno("unable to write pack header");
}

static int deflate_to_pack(struct bulk_checkin_packfile *state,
			   struct object_id *result_oid,
			   int fd, size_t size,
			   enum object_type type, const char *path,
			   unsigned flags)
{
	off_t seekback, already_hashed_to;
	git_hash_ctx ctx;
	unsigned char obuf[16384];
	unsigned header_len;
	struct hashfile_checkpoint checkpoint = {0};
	struct pack_idx_entry *idx = NULL;

	seekback = lseek(fd, 0, SEEK_CUR);
	if (seekback == (off_t) -1)
		return error("cannot find the current offset");

	header_len = format_object_header((char *)obuf, sizeof(obuf),
					  type, size);
	the_hash_algo->init_fn(&ctx);
	the_hash_algo->update_fn(&ctx, obuf, header_len);

	/* Note: idx is non-NULL when we are writing */
	if ((flags & HASH_WRITE_OBJECT) != 0)
		CALLOC_ARRAY(idx, 1);

	already_hashed_to = 0;

	while (1) {
		prepare_to_stream(state, flags);
		if (idx) {
			hashfile_checkpoint(state->f, &checkpoint);
			idx->offset = state->offset;
			crc32_begin(state->f);
		}
		if (!stream_to_pack(state, &ctx, &already_hashed_to,
				    fd, size, type, path, flags))
			break;
		/*
		 * Writing this object to the current pack will make
		 * it too big; we need to truncate it, start a new
		 * pack, and write into it.
		 */
		if (!idx)
			BUG("should not happen");
		hashfile_truncate(state->f, &checkpoint);
		state->offset = checkpoint.offset;
		flush_bulk_checkin_packfile(state);
		if (lseek(fd, seekback, SEEK_SET) == (off_t) -1)
			return error("cannot seek back");
	}
	the_hash_algo->final_oid_fn(result_oid, &ctx);
	if (!idx)
		return 0;

	idx->crc32 = crc32_end(state->f);
	if (already_written(state, result_oid)) {
		hashfile_truncate(state->f, &checkpoint);
		state->offset = checkpoint.offset;
		free(idx);
	} else {
		oidcpy(&idx->oid, result_oid);
		ALLOC_GROW(state->written,
			   state->nr_written + 1,
			   state->alloc_written);
		state->written[state->nr_written++] = idx;
	}
	return 0;
}

void prepare_loose_object_bulk_checkin(void)
{
	/*
	 * We lazily create the temporary object directory
	 * the first time an object might be added, since
	 * callers may not know whether any objects will be
	 * added at the time they call begin_odb_transaction.
	 */
	if (!odb_transaction_nesting || bulk_fsync_objdir)
		return;

	bulk_fsync_objdir = tmp_objdir_create("bulk-fsync");
	if (bulk_fsync_objdir)
		tmp_objdir_replace_primary_odb(bulk_fsync_objdir, 0);
}

void fsync_loose_object_bulk_checkin(int fd, const char *filename)
{
	/*
	 * If we have an active ODB transaction, we issue a call that
	 * cleans the filesystem page cache but avoids a hardware flush
	 * command. Later on we will issue a single hardware flush
	 * before renaming the objects to their final names as part of
	 * flush_batch_fsync.
	 */
	if (!bulk_fsync_objdir ||
	    git_fsync(fd, FSYNC_WRITEOUT_ONLY) < 0) {
		fsync_or_die(fd, filename);
	}
}

int index_bulk_checkin(struct object_id *oid,
		       int fd, size_t size, enum object_type type,
		       const char *path, unsigned flags)
{
	int status = deflate_to_pack(&bulk_checkin_packfile, oid, fd, size, type,
				     path, flags);
	if (!odb_transaction_nesting)
		flush_bulk_checkin_packfile(&bulk_checkin_packfile);
	return status;
}

void begin_odb_transaction(void)
{
	odb_transaction_nesting += 1;
}

void flush_odb_transaction(void)
{
	flush_batch_fsync();
	flush_bulk_checkin_packfile(&bulk_checkin_packfile);
}

void end_odb_transaction(void)
{
	odb_transaction_nesting -= 1;
	if (odb_transaction_nesting < 0)
		BUG("Unbalanced ODB transaction nesting");

	if (odb_transaction_nesting)
		return;

	flush_odb_transaction();
}