Use 'skip' when ignoring data in tar archives. This dramatically

increases performance when extracting a single entry from a large
uncompressed archive, especially on slow devices such as USB hard
drives.

Requires a number of changes:
   * New archive_read_open2() supports a 'skip' client function
   * Old archive_read_open() is implemented as a wrapper now, to
     continue supporting the old API/ABI.
   * _read_open_fd and _read_open_file sprout new 'skip' functions.
   * compression layer gets a new 'skip' operation.
   * compression_none passes skip requests through to client.
   * compression_{gzip,bzip2,compress} simply ignore skip requests.

Thanks to: Benjamin Lutz, who designed and implemented the whole thing.
   I'm just committing it.  ;-)

TODO: Need to update the documentation a little bit.

1 files changed, 15 insertions, 0 deletions

diff --git a/lib/libarchive/archive_read.c b/lib/libarchive/archive_read.c
index c6e47e1..46ccb59 100644
--- a/lib/libarchive/archive_read.c
+++ b/lib/libarchive/archive_read.c
@@ -110,6 +110,19 @@ archive_read_open(struct archive *a, void *client_data,
     archive_open_callback *client_opener, archive_read_callback *client_reader,
     archive_close_callback *client_closer)
 {
+	/* Old archive_read_open() is just a thin shell around
+	 * archive_read_open2. */
+	return archive_read_open2(a, client_data, client_opener,
+	    client_reader, NULL, client_closer);
+}
+
+int
+archive_read_open2(struct archive *a, void *client_data,
+    archive_open_callback *client_opener,
+    archive_read_callback *client_reader,
+    archive_skip_callback *client_skipper,
+    archive_close_callback *client_closer)
+{
 	const void *buffer;
 	ssize_t bytes_read;
 	int high_bidder;
@@ -129,6 +142,7 @@ archive_read_open(struct archive *a, void *client_data,
 	 */
 	a->client_opener = NULL;
 	a->client_reader = NULL;
+	a->client_skipper = NULL;
 	a->client_closer = NULL;
 	a->client_data = NULL;
 
@@ -167,6 +181,7 @@ archive_read_open(struct archive *a, void *client_data,
 	/* Now that the client callbacks have worked, remember them. */
 	a->client_opener = client_opener; /* Do we need to remember this? */
 	a->client_reader = client_reader;
+	a->client_skipper = client_skipper;
 	a->client_closer = client_closer;
 	a->client_data = client_data;