struct snapshot: store `start` rather than `header_len`

Store a pointer to the start of the actual references within the
`packed-refs` contents rather than storing the length of the header.
This is more convenient for most users of this field.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index dab8a85d9a67870d45e160e66ab382991a181eae..26b890118cb1de1335ee5ba388645516b5446dcf 100644 (file)
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -68,17 +68,21 @@ struct snapshot {
        int mmapped;
 
        /*
-        * The contents of the `packed-refs` file. If the file was
-        * already sorted, this points at the mmapped contents of the
-        * file. If not, this points at heap-allocated memory
-        * containing the contents, sorted. If there were no contents
-        * (e.g., because the file didn't exist), `buf` and `eof` are
-        * both NULL.
+        * The contents of the `packed-refs` file:
+        *
+        * - buf -- a pointer to the start of the memory
+        * - start -- a pointer to the first byte of actual references
+        *   (i.e., after the header line, if one is present)
+        * - eof -- a pointer just past the end of the reference
+        *   contents
+        *
+        * If the `packed-refs` file was already sorted, `buf` points
+        * at the mmapped contents of the file. If not, it points at
+        * heap-allocated memory containing the contents, sorted. If
+        * there were no contents (e.g., because the file didn't
+        * exist), `buf`, `start`, and `eof` are all NULL.
         */
-       char *buf, *eof;
-
-       /* The size of the header line, if any; otherwise, 0: */
-       size_t header_len;
+       char *buf, *start, *eof;
 
        /*
         * What is the peeled state of the `packed-refs` file that
@@ -169,8 +173,7 @@ static void clear_snapshot_buffer(struct snapshot *snapshot)
        } else {
                free(snapshot->buf);
        }
-       snapshot->buf = snapshot->eof = NULL;
-       snapshot->header_len = 0;
+       snapshot->buf = snapshot->start = snapshot->eof = NULL;
 }
 
 /*
@@ -319,13 +322,14 @@ static void sort_snapshot(struct snapshot *snapshot)
        size_t len, i;
        char *new_buffer, *dst;
 
-       pos = snapshot->buf + snapshot->header_len;
+       pos = snapshot->start;
        eof = snapshot->eof;
-       len = eof - pos;
 
-       if (!len)
+       if (pos == eof)
                return;
 
+       len = eof - pos;
+
        /*
         * Initialize records based on a crude estimate of the number
         * of references in the file (we'll grow it below if needed):
@@ -391,9 +395,8 @@ static void sort_snapshot(struct snapshot *snapshot)
         * place:
         */
        clear_snapshot_buffer(snapshot);
-       snapshot->buf = new_buffer;
+       snapshot->buf = snapshot->start = new_buffer;
        snapshot->eof = new_buffer + len;
-       snapshot->header_len = 0;
 
 cleanup:
        free(records);
@@ -442,14 +445,14 @@ static const char *find_end_of_record(const char *p, const char *end)
  */
 static void verify_buffer_safe(struct snapshot *snapshot)
 {
-       const char *buf = snapshot->buf + snapshot->header_len;
+       const char *start = snapshot->start;
        const char *eof = snapshot->eof;
        const char *last_line;
 
-       if (buf == eof)
+       if (start == eof)
                return;
 
-       last_line = find_start_of_record(buf, eof - 1);
+       last_line = find_start_of_record(start, eof - 1);
        if (*(eof - 1) != '\n' || eof - last_line < GIT_SHA1_HEXSZ + 2)
                die_invalid_line(snapshot->refs->path,
                                 last_line, eof - last_line);
@@ -495,18 +498,19 @@ static int load_contents(struct snapshot *snapshot)
                bytes_read = read_in_full(fd, snapshot->buf, size);
                if (bytes_read < 0 || bytes_read != size)
                        die_errno("couldn't read %s", snapshot->refs->path);
-               snapshot->eof = snapshot->buf + size;
                snapshot->mmapped = 0;
                break;
        case MMAP_TEMPORARY:
        case MMAP_OK:
                snapshot->buf = xmmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
-               snapshot->eof = snapshot->buf + size;
                snapshot->mmapped = 1;
                break;
        }
        close(fd);
 
+       snapshot->start = snapshot->buf;
+       snapshot->eof = snapshot->buf + size;
+
        return 1;
 }
 
@@ -539,7 +543,7 @@ static const char *find_reference_location(struct snapshot *snapshot,
         * preceding records all have reference names that come
         * *before* `refname`.
         */
-       const char *lo = snapshot->buf + snapshot->header_len;
+       const char *lo = snapshot->start;
 
        /*
         * A pointer to a the first character of a record whose
@@ -617,8 +621,7 @@ static struct snapshot *create_snapshot(struct packed_ref_store *refs)
        /* If the file has a header line, process it: */
        if (snapshot->buf < snapshot->eof && *snapshot->buf == '#') {
                struct strbuf tmp = STRBUF_INIT;
-               char *p;
-               const char *eol;
+               char *p, *eol;
                struct string_list traits = STRING_LIST_INIT_NODUP;
 
                eol = memchr(snapshot->buf, '\n',
@@ -647,7 +650,7 @@ static struct snapshot *create_snapshot(struct packed_ref_store *refs)
                /* perhaps other traits later as well */
 
                /* The "+ 1" is for the LF character. */
-               snapshot->header_len = eol + 1 - snapshot->buf;
+               snapshot->start = eol + 1;
 
                string_list_clear(&traits, 0);
                strbuf_release(&tmp);
@@ -671,13 +674,12 @@ static struct snapshot *create_snapshot(struct packed_ref_store *refs)
                 * We don't want to leave the file mmapped, so we are
                 * forced to make a copy now:
                 */
-               size_t size = snapshot->eof -
-                       (snapshot->buf + snapshot->header_len);
+               size_t size = snapshot->eof - snapshot->start;
                char *buf_copy = xmalloc(size);
 
-               memcpy(buf_copy, snapshot->buf + snapshot->header_len, size);
+               memcpy(buf_copy, snapshot->start, size);
                clear_snapshot_buffer(snapshot);
-               snapshot->buf = buf_copy;
+               snapshot->buf = snapshot->start = buf_copy;
                snapshot->eof = buf_copy + size;
        }
 
@@ -937,7 +939,7 @@ static struct ref_iterator *packed_ref_iterator_begin(
        if (prefix && *prefix)
                start = find_reference_location(snapshot, prefix, 0);
        else
-               start = snapshot->buf + snapshot->header_len;
+               start = snapshot->start;
 
        iter->pos = start;
        iter->eof = snapshot->eof;