[PATCH 08/11] streaming_write_entry(): support files with holes

[Junio C Hamano <gitster@pobox.com>]

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>
---
 entry.c |   18 +++++++++++++++++-
 1 files changed, 17 insertions(+), 1 deletions(-)

diff --git a/entry.c b/entry.c
index 7733a6b..d50e388 100644
--- 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);
@@ -137,17 +138,32 @@ static int streaming_write_entry(struct cache_entry *ce, char *path,
 
 	for (;;) {
 		char buf[10240];
-		ssize_t wrote;
+		ssize_t wrote, holeto;
 		ssize_t readlen = read_istream(st, buf, sizeof(buf));
 
 		if (!readlen)
 			break;
+		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:
-- 
1.7.5.1.365.g32b65