libpayload: cbfs: Add cbfs_handle API for more fine-grained accesses

The libpayload CBFS APIs are pretty old and clunky, primarily because of
the way the cbfs_media struct may or may not be passed in and may be
initialized inside the API calls in a way that cannot be passed back out
again. Due to this, the only real CBFS access function we have always
reads a whole file with all metadata, and everything else has to build
on top of that. This makes certain tasks like reading just a file
attribute very inefficient on non-memory-mapped platforms (because you
always have to map the whole file).

This patch isn't going to fix the world, but will allow a bit more
flexibility by bolting a new API on top which uses a struct cbfs_handle
to represent a found but not yet read file. A cbfs_handle contains a
copy of the cbfs_media needed to read the file, so it can be kept and
passed around to read individual parts of it after the initial lookup.
The existing (non-media) legacy API is retained for backwards
compatibility, as is cbfs_file_get_contents() (which is most likely what
more recent payloads would have used, and also a good convenience
wrapper for the most simple use case), but they are now implemented on
top of the new API.

TEST=Booted Oak, made sure that firmware screens and software sync
worked okay.

Change-Id: I269f3979e77ae691ee9d4e1ab564eff6d45b7cbe
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/14810
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

1 files changed, 16 insertions, 1 deletions

diff --git a/payloads/libpayload/libcbfs/cbfs.c b/payloads/libpayload/libcbfs/cbfs.c
index a1cc7e443c..38b1ff8c71 100644
--- a/payloads/libpayload/libcbfs/cbfs.c
+++ b/payloads/libpayload/libcbfs/cbfs.c
@@ -159,7 +159,22 @@ void *cbfs_load_payload(struct cbfs_media *media, const char *name)
 }
 
 struct cbfs_file *cbfs_find(const char *name) {
-	return cbfs_get_file(CBFS_DEFAULT_MEDIA, name);
+	struct cbfs_handle *handle = cbfs_get_handle(CBFS_DEFAULT_MEDIA, name);
+	struct cbfs_media *m = &handle->media;
+	void *ret;
+
+	if (!handle)
+		return NULL;
+
+	ret = m->map(m, handle->media_offset,
+		     handle->content_offset + handle->content_size);
+	if (ret == CBFS_MEDIA_INVALID_MAP_ADDRESS) {
+		free(handle);
+		return NULL;
+	}
+
+	free(handle);
+	return ret;
 }
 
 void *cbfs_find_file(const char *name, int type) {