Re: [PATCH] FIT: add first support for compressed images

[Sascha Hauer <sha@pengutronix.de>]

On Mon, Aug 08, 2022 at 01:38:28PM +0200, Ahmad Fatoum wrote:
> Hello Sascha,
> 
> On 08.08.22 13:11, Sascha Hauer wrote:
> > On Mon, Aug 08, 2022 at 08:56:48AM +0200, Ahmad Fatoum wrote:
> >> 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>
> >> ---
> >>  common/image-fit.c   | 38 +++++++++++++++++++++++++++++++++++---
> >>  include/uncompress.h |  6 ++++++
> >>  lib/uncompress.c     | 40 ++++++++++++++++++++++++++++++++++++++++
> >>  3 files changed, 81 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/common/image-fit.c b/common/image-fit.c
> >> index 507a857cadb4..e692fcdaa737 100644
> >> --- a/common/image-fit.c
> >> +++ b/common/image-fit.c
> >> @@ -21,6 +21,7 @@
> >>  #include <linux/err.h>
> >>  #include <stringlist.h>
> >>  #include <rsa.h>
> >> +#include <uncompress.h>
> >>  #include <image-fit.h>
> >>  
> >>  #define FDT_MAX_DEPTH 32
> >> @@ -559,6 +560,11 @@ int fit_get_image_address(struct fit_handle *handle, void *configuration,
> >>  	return ret;
> >>  }
> >>  
> >> +static void fit_uncompress_error_fn(char *x)
> >> +{
> >> +	pr_err("%s\n", x);
> >> +}
> >> +
> >>  /**
> >>   * fit_open_image - Open an image in a FIT image
> >>   * @handle: The FIT image handle
> >> @@ -581,8 +587,10 @@ int fit_open_image(struct fit_handle *handle, void *configuration,
> >>  		   unsigned long *outsize)
> >>  {
> >>  	struct device_node *image;
> >> -	const char *unit = name, *type = NULL, *desc= "(no description)";
> >> -	const void *data;
> >> +	const char *unit = name, *type = NULL, *compression = NULL,
> >> +	      *desc= "(no description)";
> >> +	struct property *dataprop;
> >> +	const void *data = NULL;
> >>  	int data_len;
> >>  	int ret = 0;
> >>  
> >> @@ -599,7 +607,9 @@ int fit_open_image(struct fit_handle *handle, void *configuration,
> >>  		return -EINVAL;
> >>  	}
> >>  
> >> -	data = of_get_property(image, "data", &data_len);
> >> +	dataprop = of_find_property(image, "data", &data_len);
> >> +	if (dataprop)
> >> +		data = of_property_get_value(dataprop);
> >>  	if (!data) {
> >>  		pr_err("data not found\n");
> >>  		return -EINVAL;
> >> @@ -613,6 +623,28 @@ int fit_open_image(struct fit_handle *handle, void *configuration,
> >>  	if (ret < 0)
> >>  		return ret;
> >>  
> >> +	of_property_read_string(image, "compression", &compression);
> >> +	if (compression && strcmp(compression, "none") != 0) {
> >> +		if (!IS_ENABLED(CONFIG_UNCOMPRESS)) {
> >> +			pr_err("image has compression = \"%s\", but support not compiled in\n");
> >> +			return -ENOSYS;
> >> +		}
> >> +		if (!dataprop->value) {
> >> +			void *uc_data;
> >> +
> >> +			data_len = uncompress_buf_to_buf(data, data_len, &uc_data,
> >> +						    fit_uncompress_error_fn);
> >> +			if (data_len < 0) {
> >> +				pr_err("data couldn't be decompressed\n");
> >> +				return data_len;
> >> +			}
> >> +
> >> +			/* associate buffer with FIT, so it's not leaked */
> >> +			data = dataprop->value = uc_data;
> >> +			dataprop->length = data_len;
> > 
> > Why are you fiddling with struct property fields directly?
> > of_get_property() and of_set_property() should do what you want.
> 
> of_set_property copies the data into a new buffer, which I want
> to avoid doing again.

Ah, yes. Ok then.

Still the

	if (!dataprop->value) {
		...
	}

part confuses me. With the current code it won't be set. If it will be
set due to future changes then your code won't uncompress the buffer and
silently continues. I think this should rather be

	free(dataprop->value);
	dataprop->value = uc_data;

As a bonus you'll save an indention level.

Sascha

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