Fix 'bsdtar -t' on tape drives. Libarchive uses the

skip() callback to skip over data when reading uncompressed
archives.  This gets invoked, for example, during tar -t
or tar -x with a filename argument.  The revised code
only calls [lf]seek() on regular files, instead of depending
on the kernel to return an error.

Thanks to: bde for explaining the implementation of lseek()
Thanks to: Daniel O'Connor for testing
Approved by: re (Ken Smith)
MFC after: 5 days

1 files changed, 13 insertions, 2 deletions

diff --git a/lib/libarchive/archive_read_open_fd.c b/lib/libarchive/archive_read_open_fd.c
index 0608fd6..13afe63 100644
--- a/lib/libarchive/archive_read_open_fd.c
+++ b/lib/libarchive/archive_read_open_fd.c
@@ -78,7 +78,8 @@ archive_read_open_fd(struct archive *a, int fd, size_t block_size)
 		return (ARCHIVE_FATAL);
 	}
 	mine->fd = fd;
-	mine->can_skip = 1;
+	/* lseek() hardly ever works, so disable it by default.  See below. */
+	mine->can_skip = 0;
 	return (archive_read_open2(a, mine, file_open, file_read, file_skip, file_close));
 }
 
@@ -93,8 +94,18 @@ file_open(struct archive *a, void *client_data)
 		return (ARCHIVE_FATAL);
 	}
 
-	if (S_ISREG(st.st_mode))
+	if (S_ISREG(st.st_mode)) {
 		archive_read_extract_set_skip_file(a, st.st_dev, st.st_ino);
+		/*
+		 * Enabling skip here is a performance optimization for
+		 * anything that supports lseek().  On FreeBSD, only
+		 * regular files and raw disk devices support lseek() and
+		 * there's no portable way to determine if a device is
+		 * a raw disk device, so we only enable this optimization
+		 * for regular files.
+		 */
+		mine->can_skip = 1;
+	}
 	return (ARCHIVE_OK);
 }