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

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hello Sascha,

On 08.08.22 14:03, Sascha Hauer wrote:
> 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.

I don't want to free dataprop->value. I want to cache the uncompressed
data alongside the FIT, so a renewed call to fit_open_image()
doesn't decompress again. I haven't checked if this can happen currently,
but it feels natural to keep value_const for the uncompressed data
and populate value with the compressed data and do the uncompression
only once on first fit_open_image().

Cheers,
Ahmad


> 
> Sascha
> 


-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |