Re: [PATCH 4/5] erofs: refine z_erofs_transform_plain() for sub-page block support

[Yue Hu <zbestahu@gmail.com>]

On Wed,  6 Dec 2023 17:10:56 +0800
Gao Xiang <hsiangkao@linux.alibaba.com> wrote:

> Sub-page block support is still unusable even with previous commits if
> interlaced PLAIN pclusters exist.  Such pclusters can be found if the
> fragment feature is enabled.
> 
> This commit tries to handle "the head part" of interlaced PLAIN
> pclusters first: it was once explained in commit fdffc091e6f9 ("erofs:
> support interlaced uncompressed data for compressed files").
> 
> It uses a unique way for both shifted and interlaced PLAIN pclusters.
> As an added bonus, PLAIN pclusters larger than the block size is also
> supported now for the upcoming large lclusters.
> 
> Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
> ---
>  fs/erofs/decompressor.c | 81 ++++++++++++++++++++++++-----------------
>  1 file changed, 48 insertions(+), 33 deletions(-)
> 
> diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
> index 021be5feb1bc..5ec11f5024b7 100644
> --- a/fs/erofs/decompressor.c
> +++ b/fs/erofs/decompressor.c
> @@ -319,43 +319,58 @@ static int z_erofs_lz4_decompress(struct z_erofs_decompress_req *rq,
>  static int z_erofs_transform_plain(struct z_erofs_decompress_req *rq,
>  				   struct page **pagepool)
>  {
> -	const unsigned int inpages = PAGE_ALIGN(rq->inputsize) >> PAGE_SHIFT;
> -	const unsigned int outpages =
> +	const unsigned int nrpages_in =
> +		PAGE_ALIGN(rq->pageofs_in + rq->inputsize) >> PAGE_SHIFT;
> +	const unsigned int nrpages_out =
>  		PAGE_ALIGN(rq->pageofs_out + rq->outputsize) >> PAGE_SHIFT;
> -	const unsigned int righthalf = min_t(unsigned int, rq->outputsize,
> -					     PAGE_SIZE - rq->pageofs_out);
> -	const unsigned int lefthalf = rq->outputsize - righthalf;
> -	const unsigned int interlaced_offset =
> -		rq->alg == Z_EROFS_COMPRESSION_SHIFTED ? 0 : rq->pageofs_out;
> -	u8 *src;
> -
> -	if (outpages > 2 && rq->alg == Z_EROFS_COMPRESSION_SHIFTED) {
> -		DBG_BUGON(1);
> -		return -EFSCORRUPTED;
> -	}
> -
> -	if (rq->out[0] == *rq->in) {
> -		DBG_BUGON(rq->pageofs_out);
> -		return 0;
> +	const unsigned int bs = rq->sb->s_blocksize;
> +	unsigned int cur = 0, ni = 0, no, pi, po, insz, cnt;
> +	u8 *kin;
> +
> +	DBG_BUGON(rq->outputsize > rq->inputsize);
> +	if (rq->alg == Z_EROFS_COMPRESSION_INTERLACED) {
> +		cur = bs - (rq->pageofs_out & (bs - 1));
> +		pi = (rq->pageofs_in + rq->inputsize - cur) & ~PAGE_MASK;
> +		cur = min(cur, rq->outputsize);
> +		if (cur && rq->out[0]) {
> +			kin = kmap_local_page(rq->in[nrpages_in - 1]);
> +			if (rq->out[0] == rq->in[nrpages_in - 1]) {
> +				memmove(kin + rq->pageofs_out, kin + pi, cur);
> +				flush_dcache_page(rq->out[0]);
> +			} else {
> +				memcpy_to_page(rq->out[0], rq->pageofs_out,
> +					       kin + pi, cur);
> +			}
> +			kunmap_local(kin);
> +		}
> +		rq->outputsize -= cur;
>  	}
>  
> -	src = kmap_local_page(rq->in[inpages - 1]) + rq->pageofs_in;
> -	if (rq->out[0])
> -		memcpy_to_page(rq->out[0], rq->pageofs_out,
> -			       src + interlaced_offset, righthalf);
> -
> -	if (outpages > inpages) {
> -		DBG_BUGON(!rq->out[outpages - 1]);
> -		if (rq->out[outpages - 1] != rq->in[inpages - 1]) {
> -			memcpy_to_page(rq->out[outpages - 1], 0, src +
> -					(interlaced_offset ? 0 : righthalf),
> -				       lefthalf);
> -		} else if (!interlaced_offset) {
> -			memmove(src, src + righthalf, lefthalf);
> -			flush_dcache_page(rq->in[inpages - 1]);
> -		}
> +	for (; rq->outputsize; rq->pageofs_in = 0, cur += PAGE_SIZE, ni++) {
> +		insz = min(PAGE_SIZE - rq->pageofs_in, rq->outputsize);

min_t(unsigned int, ,)?

../include/linux/minmax.h:21:28: error: comparison of distinct pointer types lacks a cast [-Werror]
  (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))


> +		rq->outputsize -= insz;
> +		if (!rq->in[ni])
> +			continue;
> +		kin = kmap_local_page(rq->in[ni]);
> +		pi = 0;
> +		do {
> +			no = (rq->pageofs_out + cur + pi) >> PAGE_SHIFT;
> +			po = (rq->pageofs_out + cur + pi) & ~PAGE_MASK;
> +			DBG_BUGON(no >= nrpages_out);
> +			cnt = min(insz - pi, PAGE_SIZE - po);

ditto

> +			if (rq->out[no] == rq->in[ni]) {
> +				memmove(kin + po,
> +					kin + rq->pageofs_in + pi, cnt);
> +				flush_dcache_page(rq->out[no]);
> +			} else if (rq->out[no]) {
> +				memcpy_to_page(rq->out[no], po,
> +					       kin + rq->pageofs_in + pi, cnt);
> +			}
> +			pi += cnt;
> +		} while (pi < insz);
> +		kunmap_local(kin);
>  	}
> -	kunmap_local(src);
> +	DBG_BUGON(ni > nrpages_in);
>  	return 0;
>  }
>