streaming_write_entry(): support files with holes

One typical use of a large binary file is to hold a sparse on-disk hash
table with a lot of holes. Help preserving the holes with lseek().

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/entry.c b/entry.c
index da37d0151413b50dd3e4cc223f71ce55643f349b..e2dc16c13143b97b28e4bc82238bda3c899306f3 100644 (file)
--- a/entry.c
+++ b/entry.c
@@ -123,6 +123,7 @@ static int streaming_write_entry(struct cache_entry *ce, char *path,
        enum object_type type;
        unsigned long sz;
        int result = -1;
+       ssize_t kept = 0;
        int fd = -1;
 
        st = open_istream(ce->sha1, &type, &sz);
@@ -136,18 +137,34 @@ static int streaming_write_entry(struct cache_entry *ce, char *path,
                goto close_and_exit;
 
        for (;;) {
-               char buf[10240];
-               ssize_t wrote;
+               char buf[1024 * 16];
+               ssize_t wrote, holeto;
                ssize_t readlen = read_istream(st, buf, sizeof(buf));
 
                if (!readlen)
                        break;
+               if (sizeof(buf) == readlen) {
+                       for (holeto = 0; holeto < readlen; holeto++)
+                               if (buf[holeto])
+                                       break;
+                       if (readlen == holeto) {
+                               kept += holeto;
+                               continue;
+                       }
+               }
 
+               if (kept && lseek(fd, kept, SEEK_CUR) == (off_t) -1)
+                       goto close_and_exit;
+               else
+                       kept = 0;
                wrote = write_in_full(fd, buf, readlen);
 
                if (wrote != readlen)
                        goto close_and_exit;
        }
+       if (kept && (lseek(fd, kept - 1, SEEK_CUR) == (off_t) -1 ||
+                    write(fd, "", 1) != 1))
+               goto close_and_exit;
        *fstat_done = fstat_output(fd, state, statbuf);
 
 close_and_exit: