From: Derrick Stolee <dstolee@xxxxxxxxxxxxx>
In anticipation of combining the logic from the commit-graph and
multi-pack-index file formats, create a new chunk-format API. Use a
'struct chunkfile' pointer to keep track of data that has been
registered for writes. This struct is anonymous outside of
chunk-format.c to ensure no user attempts to interfere with the data.
The next change will use this API in commit-graph.c, but the general
approach is:
1. initialize the chunkfile with init_chunkfile(f).
2. add chunks in the intended writing order with add_chunk().
3. write any header information to the hashfile f.
4. write the chunkfile data using write_chunkfile().
5. free the chunkfile struct using free_chunkfile().
Helped-by: Taylor Blau <me@xxxxxxxxxxxx>
Helped-by: Junio C Hamano <gitster@xxxxxxxxx>
Signed-off-by: Derrick Stolee <dstolee@xxxxxxxxxxxxx>
---
Makefile | 1 +
chunk-format.c | 91 ++++++++++++++++++++++++++++++++++++++++++++++++++
chunk-format.h | 19 +++++++++++
3 files changed, 111 insertions(+)
create mode 100644 chunk-format.c
create mode 100644 chunk-format.h
diff --git a/Makefile b/Makefile
index 7b64106930a6..50a7663841e9 100644
--- a/Makefile
+++ b/Makefile
@@ -854,6 +854,7 @@ LIB_OBJS += bundle.o
LIB_OBJS += cache-tree.o
LIB_OBJS += chdir-notify.o
LIB_OBJS += checkout.o
+LIB_OBJS += chunk-format.o
LIB_OBJS += color.o
LIB_OBJS += column.o
LIB_OBJS += combine-diff.o
diff --git a/chunk-format.c b/chunk-format.c
new file mode 100644
index 000000000000..6e0f1900213e
--- /dev/null
+++ b/chunk-format.c
@@ -0,0 +1,91 @@
+#include "cache.h"
+#include "chunk-format.h"
+#include "csum-file.h"
+#define CHUNK_LOOKUP_WIDTH 12
+
+/*
+ * When writing a chunk-based file format, collect the chunks in
+ * an array of chunk_info structs. The size stores the _expected_
+ * amount of data that will be written by write_fn.
+ */
+struct chunk_info {
+ uint32_t id;
+ uint64_t size;
+ chunk_write_fn write_fn;
+};
+
+struct chunkfile {
+ struct hashfile *f;
+
+ struct chunk_info *chunks;
+ size_t chunks_nr;
+ size_t chunks_alloc;
+};
+
+struct chunkfile *init_chunkfile(struct hashfile *f)
+{
+ struct chunkfile *cf = xcalloc(1, sizeof(*cf));
+ cf->f = f;
+ return cf;
+}
+
+void free_chunkfile(struct chunkfile *cf)
+{
+ if (!cf)
+ return;
+ free(cf->chunks);
+ free(cf);
+}
+
+int get_num_chunks(struct chunkfile *cf)
+{
+ return cf->chunks_nr;
+}
+
+void add_chunk(struct chunkfile *cf,
+ uint32_t id,
+ size_t size,
+ chunk_write_fn fn)
+{
+ ALLOC_GROW(cf->chunks, cf->chunks_nr + 1, cf->chunks_alloc);
+
+ cf->chunks[cf->chunks_nr].id = id;
+ cf->chunks[cf->chunks_nr].write_fn = fn;
+ cf->chunks[cf->chunks_nr].size = size;
+ cf->chunks_nr++;
+}
+
+int write_chunkfile(struct chunkfile *cf, void *data)
+{
+ int i;
+ uint64_t cur_offset = hashfile_total(cf->f);
+
+ /* Add the table of contents to the current offset */
+ cur_offset += (cf->chunks_nr + 1) * CHUNK_LOOKUP_WIDTH;
+
+ for (i = 0; i < cf->chunks_nr; i++) {
+ hashwrite_be32(cf->f, cf->chunks[i].id);
+ hashwrite_be64(cf->f, cur_offset);
+
+ cur_offset += cf->chunks[i].size;
+ }
+
+ /* Trailing entry marks the end of the chunks */
+ hashwrite_be32(cf->f, 0);
+ hashwrite_be64(cf->f, cur_offset);
+
+ for (i = 0; i < cf->chunks_nr; i++) {
+ off_t start_offset = hashfile_total(cf->f);
+ int result = cf->chunks[i].write_fn(cf->f, data);
+
+ if (result)
+ return result;
+
+ if (hashfile_total(cf->f) - start_offset != cf->chunks[i].size)
+ BUG("expected to write %"PRId64" bytes to chunk %"PRIx32", but wrote %"PRId64" instead",
+ cf->chunks[i].size, cf->chunks[i].id,
+ hashfile_total(cf->f) - start_offset);
+ }
+
+ return 0;
+}
diff --git a/chunk-format.h b/chunk-format.h
new file mode 100644
index 000000000000..9a1d770accec
--- /dev/null
+++ b/chunk-format.h
@@ -0,0 +1,19 @@
+#ifndef CHUNK_FORMAT_H
+#define CHUNK_FORMAT_H
+
+#include "git-compat-util.h"
+
+struct hashfile;
+struct chunkfile;
+
+struct chunkfile *init_chunkfile(struct hashfile *f);
+void free_chunkfile(struct chunkfile *cf);
+int get_num_chunks(struct chunkfile *cf);
+typedef int (*chunk_write_fn)(struct hashfile *f, void *data);
+void add_chunk(struct chunkfile *cf,
+ uint32_t id,
+ size_t size,
+ chunk_write_fn fn);
+int write_chunkfile(struct chunkfile *cf, void *data);
+
+#endif
--
gitgitgadget
