[PATCH v3 05/21] read_packed_refs(): use mmap to read the `packed-refs` file

[Michael Haggerty]

It's still done in a pretty stupid way, involving more data copying
than necessary. That will improve in future commits.

Signed-off-by: Michael Haggerty <mhag...@alum.mit.edu>
---
 refs/packed-backend.c | 42 ++++++++++++++++++++++++++++++++----------
 1 file changed, 32 insertions(+), 10 deletions(-)

diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index 5c50c223ef..154abbd83a 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -215,8 +215,12 @@ static NORETURN void die_invalid_line(const char *path,
  */
 static struct packed_ref_cache *read_packed_refs(struct packed_ref_store *refs)
 {
-       FILE *f;
        struct packed_ref_cache *packed_refs = xcalloc(1, sizeof(*packed_refs));
+       int fd;
+       struct stat st;
+       size_t size;
+       char *buf;
+       const char *pos, *eol, *eof;
        struct ref_entry *last = NULL;
        struct strbuf line = STRBUF_INIT;
        enum { PEELED_NONE, PEELED_TAGS, PEELED_FULLY } peeled = PEELED_NONE;
@@ -227,8 +231,8 @@ static struct packed_ref_cache *read_packed_refs(struct 
packed_ref_store *refs)
        packed_refs->cache = create_ref_cache(NULL, NULL);
        packed_refs->cache->root->flag &= ~REF_INCOMPLETE;
 
-       f = fopen(refs->path, "r");
-       if (!f) {
+       fd = open(refs->path, O_RDONLY);
+       if (fd < 0) {
                if (errno == ENOENT) {
                        /*
                         * This is OK; it just means that no
@@ -241,16 +245,27 @@ static struct packed_ref_cache *read_packed_refs(struct 
packed_ref_store *refs)
                }
        }
 
-       stat_validity_update(&packed_refs->validity, fileno(f));
+       stat_validity_update(&packed_refs->validity, fd);
+
+       if (fstat(fd, &st) < 0)
+               die_errno("couldn't stat %s", refs->path);
+
+       size = xsize_t(st.st_size);
+       buf = xmmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
+       pos = buf;
+       eof = buf + size;
 
        dir = get_ref_dir(packed_refs->cache->root);
-       while (strbuf_getwholeline(&line, f, '\n') != EOF) {
+       while (pos < eof) {
                struct object_id oid;
                const char *refname;
                const char *traits;
 
-               if (!line.len || line.buf[line.len - 1] != '\n')
-                       die_unterminated_line(refs->path, line.buf, line.len);
+               eol = memchr(pos, '\n', eof - pos);
+               if (!eol)
+                       die_unterminated_line(refs->path, pos, eof - pos);
+
+               strbuf_add(&line, pos, eol + 1 - pos);
 
                if (skip_prefix(line.buf, "# pack-refs with:", &traits)) {
                        if (strstr(traits, " fully-peeled "))
@@ -258,7 +273,7 @@ static struct packed_ref_cache *read_packed_refs(struct 
packed_ref_store *refs)
                        else if (strstr(traits, " peeled "))
                                peeled = PEELED_TAGS;
                        /* perhaps other traits later as well */
-                       continue;
+                       goto next_line;
                }
 
                refname = parse_ref_line(&line, &oid);
@@ -291,11 +306,18 @@ static struct packed_ref_cache *read_packed_refs(struct 
packed_ref_store *refs)
                } else {
                        die_invalid_line(refs->path, line.buf, line.len);
                }
+
+       next_line:
+               /* The "+ 1" is for the LF character. */
+               pos = eol + 1;
+               strbuf_reset(&line);
        }
 
-       fclose(f);
-       strbuf_release(&line);
+       if (munmap(buf, size))
+               die_errno("error ummapping packed-refs file");
+       close(fd);
 
+       strbuf_release(&line);
        return packed_refs;
 }
 
-- 
2.14.1