indexer: use mmap for writing

Some OSs cannot keep their ideas about file content straight when mixing
standard IO with file mapping. As we use mmap for reading from the
packfile, let's make writing to the pack file use mmap.

src/indexer.c

@@ -34,7 +34,6 @@ struct git_indexer {
 		have_delta :1;
 	struct git_pack_header hdr;
 	struct git_pack_file *pack;
-	git_filebuf pack_file;
 	unsigned int mode;
 	git_off_t off;
 	git_off_t entry_start;
@@ -67,33 +66,18 @@ const git_oid *git_indexer_hash(const git_indexer *idx)
 	return &idx->hash;
 }
 
-static int open_pack(struct git_pack_file **out, const char *filename)
-{
-	struct git_pack_file *pack;
-
-	if (git_packfile_alloc(&pack, filename) < 0)
-		return -1;
-
-	if ((pack->mwf.fd = p_open(pack->pack_name, O_RDONLY)) < 0) {
-		giterr_set(GITERR_OS, "Failed to open packfile.");
-		git_packfile_free(pack);
-		return -1;
-	}
-
-	*out = pack;
-	return 0;
-}
-
 static int parse_header(struct git_pack_header *hdr, struct git_pack_file *pack)
 {
 	int error;
+	git_map map;
 
-	/* Verify we recognize this pack file format. */
-	if ((error = p_read(pack->mwf.fd, hdr, sizeof(*hdr))) < 0) {
-		giterr_set(GITERR_OS, "Failed to read in pack header");
+	if ((error = p_mmap(&map, sizeof(*hdr), GIT_PROT_READ, GIT_MAP_SHARED, pack->mwf.fd, 0)) < 0)
 		return error;
-	}
 
+	memcpy(hdr, map.data, sizeof(*hdr));
+	p_munmap(&map);
+
+	/* Verify we recognize this pack file format. */
 	if (hdr->hdr_signature != ntohl(PACK_SIGNATURE)) {
 		giterr_set(GITERR_INDEXER, "Wrong pack signature");
 		return -1;
@@ -124,9 +108,9 @@ int git_indexer_new(
 		void *progress_payload)
 {
 	git_indexer *idx;
-	git_buf path = GIT_BUF_INIT;
+	git_buf path = GIT_BUF_INIT, tmp_path = GIT_BUF_INIT;
 	static const char suff[] = "/pack";
-	int error;
+	int error, fd;
 
 	idx = git__calloc(1, sizeof(git_indexer));
 	GITERR_CHECK_ALLOC(idx);
@@ -140,19 +124,30 @@ int git_indexer_new(
 	if (error < 0)
 		goto cleanup;
 
-	error = git_filebuf_open(&idx->pack_file, path.ptr,
-		GIT_FILEBUF_TEMPORARY | GIT_FILEBUF_DO_NOT_BUFFER,
-		idx->mode);
+	fd = git_futils_mktmp(&tmp_path, git_buf_cstr(&path), idx->mode);
 	git_buf_free(&path);
+	if (fd < 0)
+		goto cleanup;
+
+	error = git_packfile_alloc(&idx->pack, git_buf_cstr(&tmp_path));
+	git_buf_free(&tmp_path);
+
 	if (error < 0)
 		goto cleanup;
 
+	idx->pack->mwf.fd = fd;
+	if ((error = git_mwindow_file_register(&idx->pack->mwf)) < 0)
+		goto cleanup;
+
 	*out = idx;
 	return 0;
 
 cleanup:
+	if (fd != -1)
+		p_close(fd);
+
 	git_buf_free(&path);
-	git_filebuf_cleanup(&idx->pack_file);
+	git_buf_free(&tmp_path);
 	git__free(idx);
 	return -1;
 }
@@ -429,6 +424,40 @@ static void hash_partially(git_indexer *idx, const uint8_t *data, size_t size)
 	idx->inbuf_len += size - to_expell;
 }
 
+static int write_at(git_indexer *idx, const void *data, git_off_t offset, size_t size)
+{
+	git_file fd = idx->pack->mwf.fd;
+	long page_size = git__page_size();
+	git_off_t page_start, page_offset;
+	git_map map;
+	int error;
+
+	/* the offset needs to be at the beginning of the a page boundary */
+	page_start = (offset / page_size) * page_size;
+	page_offset = offset - page_start;
+
+	if ((error = p_mmap(&map, page_offset + size, GIT_PROT_WRITE, GIT_MAP_SHARED, fd, page_start)) < 0)
+		return error;
+
+	memcpy(map.data + page_offset, data, size);
+	p_munmap(&map);
+
+	return 0;
+}
+
+static int append_to_pack(git_indexer *idx, const void *data, size_t size)
+{
+	git_off_t current_size = idx->pack->mwf.size;
+
+	/* add the extra space we need at the end */
+	if (p_ftruncate(idx->pack->mwf.fd, current_size + size) < 0) {
+		giterr_system_set(errno);
+		return -1;
+	}
+
+	return write_at(idx, data, idx->pack->mwf.size, size);
+}
+
 int git_indexer_append(git_indexer *idx, const void *data, size_t size, git_transfer_progress *stats)
 {
 	int error = -1;
@@ -440,22 +469,13 @@ int git_indexer_append(git_indexer *idx, const void *data, size_t size, git_tran
 
 	processed = stats->indexed_objects;
 
-	if ((error = git_filebuf_write(&idx->pack_file, data, size)) < 0)
+	if ((error = append_to_pack(idx, data, size)) < 0)
 		return error;
 
 	hash_partially(idx, data, (int)size);
 
 	/* Make sure we set the new size of the pack */
-	if (idx->opened_pack) {
-		idx->pack->mwf.size += size;
-	} else {
-		if ((error = open_pack(&idx->pack, idx->pack_file.path_lock)) < 0)
-			return error;
-		idx->opened_pack = 1;
-		mwf = &idx->pack->mwf;
-		if ((error = git_mwindow_file_register(&idx->pack->mwf)) < 0)
-			return error;
-	}
+	idx->pack->mwf.size += size;
 
 	if (!idx->parsed_header) {
 		unsigned int total_objects;
@@ -616,17 +636,10 @@ static int index_path(git_buf *path, git_indexer *idx, const char *suffix)
  * Rewind the packfile by the trailer, as we might need to fix the
  * packfile by injecting objects at the tail and must overwrite it.
  */
-static git_off_t seek_back_trailer(git_indexer *idx)
+static void seek_back_trailer(git_indexer *idx)
 {
-	git_off_t off;
-
-	if ((off = p_lseek(idx->pack_file.fd, -GIT_OID_RAWSZ, SEEK_CUR)) < 0)
-		return -1;
-
 	idx->pack->mwf.size -= GIT_OID_RAWSZ;
 	git_mwindow_free_all(&idx->pack->mwf);
-
-	return off;
 }
 
 static int inject_object(git_indexer *idx, git_oid *id)
@@ -642,7 +655,8 @@ static int inject_object(git_indexer *idx, git_oid *id)
 	size_t len, hdr_len;
 	int error;
 
-	entry_start = seek_back_trailer(idx);
+	seek_back_trailer(idx);
+	entry_start = idx->pack->mwf.size;
 
 	if (git_odb_read(&obj, idx->odb, id) < 0)
 		return -1;
@@ -657,7 +671,9 @@ static int inject_object(git_indexer *idx, git_oid *id)
 
 	/* Write out the object header */
 	hdr_len = git_packfile__object_header(hdr, len, git_odb_object_type(obj));
-	git_filebuf_write(&idx->pack_file, hdr, hdr_len);
+	if ((error = append_to_pack(idx, hdr, hdr_len)) < 0)
+		goto cleanup;
+
 	idx->pack->mwf.size += hdr_len;
 	entry->crc = crc32(entry->crc, hdr, (uInt)hdr_len);
 
@@ -665,13 +681,16 @@ static int inject_object(git_indexer *idx, git_oid *id)
 		goto cleanup;
 
 	/* And then the compressed object */
-	git_filebuf_write(&idx->pack_file, buf.ptr, buf.size);
+	if ((error = append_to_pack(idx, buf.ptr, buf.size)) < 0)
+		goto cleanup;
+
 	idx->pack->mwf.size += buf.size;
 	entry->crc = htonl(crc32(entry->crc, (unsigned char *)buf.ptr, (uInt)buf.size));
 	git_buf_free(&buf);
 
 	/* Write a fake trailer so the pack functions play ball */
-	if ((error = git_filebuf_write(&idx->pack_file, &foo, GIT_OID_RAWSZ)) < 0)
+
+	if ((error = append_to_pack(idx, &foo, GIT_OID_RAWSZ)) < 0)
 		goto cleanup;
 
 	idx->pack->mwf.size += GIT_OID_RAWSZ;
@@ -817,19 +836,12 @@ static int update_header_and_rehash(git_indexer *idx, git_transfer_progress *sta
 	ctx = &idx->trailer;
 
 	git_hash_ctx_init(ctx);
-	git_mwindow_free_all(mwf);
+
 
 	/* Update the header to include the numer of local objects we injected */
 	idx->hdr.hdr_entries = htonl(stats->total_objects + stats->local_objects);
-	if (p_lseek(idx->pack_file.fd, 0, SEEK_SET) < 0) {
-		giterr_set(GITERR_OS, "failed to seek to the beginning of the pack");
+	if (write_at(idx, &idx->hdr, 0, sizeof(struct git_pack_header)) < 0)
 		return -1;
-	}
-
-	if (p_write(idx->pack_file.fd, &idx->hdr, sizeof(struct git_pack_header)) < 0) {
-		giterr_set(GITERR_OS, "failed to update the pack header");
-		return -1;
-	}
 
 	/*
 	 * We now use the same technique as before to determine the
@@ -837,6 +849,7 @@ static int update_header_and_rehash(git_indexer *idx, git_transfer_progress *sta
 	 * hash_partially() keep the existing trailer out of the
 	 * calculation.
 	 */
+	git_mwindow_free_all(mwf);
 	idx->inbuf_len = 0;
 	while (hashed < mwf->size) {
 		ptr = git_mwindow_open(mwf, &w, hashed, chunk, &left);
@@ -906,13 +919,7 @@ int git_indexer_commit(git_indexer *idx, git_transfer_progress *stats)
 			return -1;
 
 		git_hash_final(&trailer_hash, &idx->trailer);
-		if (p_lseek(idx->pack_file.fd, -GIT_OID_RAWSZ, SEEK_END) < 0)
-			return -1;
-
-		if (p_write(idx->pack_file.fd, &trailer_hash, GIT_OID_RAWSZ) < 0) {
-			giterr_set(GITERR_OS, "failed to update pack trailer");
-			return -1;
-		}
+		write_at(idx, &trailer_hash, idx->pack->mwf.size - GIT_OID_RAWSZ, GIT_OID_RAWSZ);
 	}
 
 	git_vector_sort(&idx->objects);
@@ -995,14 +1002,18 @@ int git_indexer_commit(git_indexer *idx, git_transfer_progress *stats)
 
 	git_mwindow_free_all(&idx->pack->mwf);
 	/* We need to close the descriptor here so Windows doesn't choke on commit_at */
-	p_close(idx->pack->mwf.fd);
+	if (p_close(idx->pack->mwf.fd) < 0) {
+		giterr_set(GITERR_OS, "failed to close packfile");
+		goto on_error;
+	}
+
 	idx->pack->mwf.fd = -1;
 
 	if (index_path(&filename, idx, ".pack") < 0)
 		goto on_error;
+
 	/* And don't forget to rename the packfile to its new place. */
-	if (git_filebuf_commit_at(&idx->pack_file, filename.ptr) < 0)
-		return -1;
+	p_rename(idx->pack->pack_name, git_buf_cstr(&filename));
 
 	git_buf_free(&filename);
 	return 0;
@@ -1022,7 +1033,7 @@ void git_indexer_free(git_indexer *idx)
 
 	git_vector_free_deep(&idx->objects);
 
-	if (idx->pack) {
+	if (idx->pack && idx->pack->idx_cache) {
 		struct git_pack_entry *pentry;
 		kh_foreach_value(
 			idx->pack->idx_cache, pentry, { git__free(pentry); });
@@ -1032,6 +1043,5 @@ void git_indexer_free(git_indexer *idx)
 
 	git_vector_free_deep(&idx->deltas);
 	git_packfile_free(idx->pack);
-	git_filebuf_cleanup(&idx->pack_file);
 	git__free(idx);
 }

src/map.h

@@ -42,5 +42,6 @@ typedef struct { /* memory mapped buffer	*/
 
 extern int p_mmap(git_map *out, size_t len, int prot, int flags, int fd, git_off_t offset);
 extern int p_munmap(git_map *map);
+extern long git__page_size(void);
 
 #endif /* INCLUDE_map_h__ */

src/posix.c

@@ -207,6 +207,13 @@ int p_write(git_file fd, const void *buf, size_t cnt)
 
 #include "map.h"
 
+long git__page_size(void)
+{
+	/* dummy; here we don't need any alignment anyway */
+	return 4096;
+}
+
+
 int p_mmap(git_map *out, size_t len, int prot, int flags, int fd, git_off_t offset)
 {
 	GIT_MMAP_VALIDATE(out, len, prot, flags);

src/posix.h

@@ -60,6 +60,7 @@ extern int p_write(git_file fd, const void *buf, size_t cnt);
 #define p_lseek(f,n,w) lseek(f, n, w)
 #define p_close(fd) close(fd)
 #define p_umask(m) umask(m)
+#define p_ftruncate(fd, sz) ftruncate(fd, sz)
 
 extern int p_open(const char *path, int flags, ...);
 extern int p_creat(const char *path, mode_t mode);

src/unix/map.c

@@ -10,8 +10,14 @@
 
 #include "map.h"
 #include <sys/mman.h>
+#include <unistd.h>
 #include <errno.h>
 
+long git__page_size(void)
+{
+	return sysconf(_SC_PAGE_SIZE);
+}
+
 int p_mmap(git_map *out, size_t len, int prot, int flags, int fd, git_off_t offset)
 {
 	int mprot = 0;

src/win32/map.c

@@ -23,6 +23,11 @@ static DWORD get_page_size(void)
 	return page_size;
 }
 
+long git__page_size(void)
+{
+	return (long)get_page_size();
+}
+
 int p_mmap(git_map *out, size_t len, int prot, int flags, int fd, git_off_t offset)
 {
 	HANDLE fh = (HANDLE)_get_osfhandle(fd);