FIT: add first support for compressed images

FIT image contents are often compressed, but we got by so far, because
a compressed initramfs is usually meant to be decompressed by the kernel
(and so has compression = "none") and arm32 kernels had their own
decompresser embedded. On ARM64, bootloader is responsible for
uncompressing kernel, so we should properly process the compression
property we so far ignored.

The decompression isn't as efficient as one would hope for, because
the FIT format only describes length of the compressed data. We thus
have two options:

  - define an output size up-front, e.g. by guessing the uncompressed
     buffer size for decompression or hardcoding it (e.g. U-Boot's
     CONFIG_SYS_BOOTM_LEN).

  -  Uncompress to a file descriptor

We choose the second one to play it safe, but it comes with worse
performance because of extra memory copies. Intention is to go with
first option for the kernel image: We know how much size we can spare
for the kernel image and can have bootm_load_os uncompress there
directly without intermittent memory copies. This would involve slight
change to the barebox decompresser API to align it with the kernel's,
which allows to have it accept and observe an output buffer size.
So far, we had the kernel PREBOOT API, which lacks such a parameter,
but that's an optimization for another day.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.barebox.org/20220809091946.3906847-1-a.fatoum@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 40 insertions, 0 deletions

diff --git a/lib/uncompress.c b/lib/uncompress.c
index 5c0d1e9f4d..0608e9f9d3 100644
--- a/lib/uncompress.c
+++ b/lib/uncompress.c
@@ -172,3 +172,43 @@ int uncompress_fd_to_buf(int infd, void *output,
 
 	return uncompress(NULL, 0, fill_fd, NULL, output, NULL, error_fn);
 }
+
+int uncompress_buf_to_fd(const void *input, size_t input_len,
+			 int outfd, void(*error_fn)(char *x))
+{
+	uncompress_outfd = outfd;
+
+	return uncompress((void *)input, input_len, NULL, flush_fd,
+			  NULL, NULL, error_fn);
+}
+
+ssize_t uncompress_buf_to_buf(const void *input, size_t input_len,
+			      void **buf, void(*error_fn)(char *x))
+{
+	char *dstpath;
+	size_t size;
+	int outfd, ret;
+
+	dstpath = make_temp("data-uncompressed");
+	if (!dstpath)
+		return -ENOMEM;
+
+	outfd = open(dstpath, O_CREAT | O_WRONLY);
+	if (outfd < 0) {
+		ret = -ENODEV;
+		goto free_temp;
+	}
+
+	ret = uncompress_buf_to_fd(input, input_len, outfd, uncompress_err_stdout);
+	if (ret)
+		goto close_outfd;
+
+	*buf = read_file(dstpath, &size);
+close_outfd:
+	close(outfd);
+	unlink(dstpath);
+free_temp:
+	free(dstpath);
+
+	return ret ?: size;
+}