Re: [PATCH 2/2] uncompress: add Android sparse image support

[Sascha Hauer <sha@pengutronix.de>]

On Sat, Sep 16, 2023 at 06:01:15PM +0200, Uwe Kleine-König wrote:
> On Thu, Sep 14, 2023 at 11:58:59AM +0200, Juergen Borleis wrote:
> > An Android sparse image file generated by the 'genimage' tool can be seen as a
> > kind of compression, since it contains only the data which should really be
> > written to a device.
> > 
> > This implementation writes only the intended content and skips anything else.
> > 
> > Signed-off-by: Juergen Borleis <jbe@pengutronix.de>
> 
> Tested-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> 
> while this obviously works, I still have a comment below:
> 
> > ---
> >  lib/uncompress.c | 82 +++++++++++++++++++++++++++++++++++++++++++++---
> >  1 file changed, 78 insertions(+), 4 deletions(-)
> > 
> > diff --git a/lib/uncompress.c b/lib/uncompress.c
> > index 0608e9f..f17e9ce 100644
> > --- a/lib/uncompress.c
> > +++ b/lib/uncompress.c
> > @@ -25,6 +25,10 @@
> >  #include <malloc.h>
> >  #include <fs.h>
> >  #include <libfile.h>
> > +#ifdef CONFIG_IMAGE_SPARSE
> > +#include <image-sparse.h>
> > +#include <linux/sizes.h>
> > +#endif
> >  
> >  static void *uncompress_buf;
> >  static unsigned int uncompress_size;
> > @@ -60,6 +64,71 @@ static int uncompress_fill(void *buf, unsigned int len)
> >  	return total;
> >  }
> >  
> > +#ifdef CONFIG_IMAGE_SPARSE
> > +static int uncompress_sparse(int source, int destination)
> > +{
> > +	int ret = 0;
> > +	struct sparse_image_ctx *sparse;
> > +
> > +	/* rewind after checking the file type */
> > +	lseek(source, 0, SEEK_SET);
> > +
> > +	sparse = sparse_image_fd(source);
> > +	if (IS_ERR(sparse)) {
> > +		pr_err("Failed to open or interpret sparse image file: %m\n");
> > +		ret = 1;
> > +		goto on_error_dev;
> > +	}
> > +
> > +	const size_t transfer_buffer_length = SZ_128K;
> > +	unsigned char *buf = malloc(transfer_buffer_length);
> > +	if (!buf) {
> > +		pr_err("Failed to alloc memory for the transfers\n");
> > +		ret = 1;
> > +		goto on_error_sparse;
> > +	}
> > +
> > +	while (1) {
> > +		loff_t write_offset;
> > +		size_t write_length;
> > +
> > +		int rc = sparse_image_read(sparse, buf, &write_offset, transfer_buffer_length, &write_length);
> > +		if (rc) {
> > +			ret = 1;
> > +			goto on_error_memory;
> > +		}
> > +		if (!write_length)
> > +			break;
> > +
> > +		discard_range(destination, write_length, write_offset);
> > +
> > +		write_offset = lseek(destination, write_offset, SEEK_SET);
> > +		if (write_offset == -1) {
> > +			pr_err("Failed to set next data's destination offset: %m\n");
> > +			ret = 1;
> > +			goto on_error_memory;
> > +
> > +		}
> > +
> > +		rc = write_full(destination, buf, write_length);
> > +		if (rc < 0) {
> > +			pr_err("Failed to write destination's next data: %m\n");
> > +			ret = 1;
> > +			goto on_error_memory;
> > +		}
> > +	}
> > +
> > +on_error_memory:
> > +	free(buf);
> > +on_error_sparse:
> > +	free(sparse); /* Note: sparse_image_close(sparse); would also close the input file descriptor */
> > +on_error_dev:
> > +	return ret;
> > +}
> > +#endif
> > +
> > +static int uncompress_infd, uncompress_outfd;
> > +
> >  int uncompress(unsigned char *inbuf, int len,
> >  	   int(*fill)(void*, unsigned int),
> >  	   int(*flush)(void*, unsigned int),
> > @@ -121,6 +190,10 @@ int uncompress(unsigned char *inbuf, int len,
> >  	case filetype_xz_compressed:
> >  		compfn = decompress_unxz;
> >  		break;
> > +#endif
> > +#ifdef CONFIG_IMAGE_SPARSE
> > +	case filetype_android_sparse:
> > +		break;
> >  #endif
> >  	default:
> >  		err = basprintf("cannot handle filetype %s",
> > @@ -131,16 +204,17 @@ int uncompress(unsigned char *inbuf, int len,
> >  		goto err;
> >  	}
> >  
> > -	ret = compfn(inbuf, len, fill ? uncompress_fill : NULL,
> > -			flush, output, pos, error_fn);
> > +	if (ft == filetype_android_sparse)
> > +		ret = uncompress_sparse(uncompress_infd, uncompress_outfd);
> > +	else
> > +		ret = compfn(inbuf, len, fill ? uncompress_fill : NULL,
> > +			     flush, output, pos, error_fn);
> 
> Wouldn't it be more natural to make uncompress_sparse use the same
> prototype as the other uncompress functions and then just have:
> 
> #ifdef CONFIG_IMAGE_SPARSE
> 	case filetype_android_sparse:
> 		compfn = decompress_sparse;
> 		break;
> #endif
> 
> Without the need to adapt the compfn call?

compfn() doesn't have access to the file descriptors which the current
sparse implementation needs.

It would be great though to let our sparse image support use an input
buffer and a fill() function.

Sascha

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