1 // SPDX-License-Identifier: GPL-2.0-only
11  * MS-SMB2 "3.1.4.4 Compressing the Message"
12  * MS-SMB2 "3.1.5.3 Decompressing the Chained Message"
13  * MS-XCA - for details of the supported algorithms
39  * Parsing the sample goes from "low-hanging fruits" (fastest algorithms, likely compressible)
48  * has_low_entropy() - Compute Shannon entropy of the sampled data.
66 	size_t i, p, p2, len, sum = 0;  in has_low_entropy()  local
69 	len = ilog2(pow4(slen));  in has_low_entropy()
74 		sum += p * (len - p2);  in has_low_entropy()
86  * calc_byte_distribution() - Compute byte distribution on the sampled data.
91  * BYTE_DIST_BAD:	A "hard no" for compression -- a computed uniform distribution of
132 			/* Too many non-ASCII (0-63) bytes. */  in is_mostly_ascii()
139 static bool has_repeated_data(const u8 *sample, size_t len)  in has_repeated_data()  argument
141 	size_t s = len / 2;  in has_repeated_data()
151 	if (a->count > b->count)  in cmp_bkt()
152 		return -1;  in cmp_bkt()
162 static int collect_sample(const struct iov_iter *iter, ssize_t max, u8 *sample)  in collect_sample()  argument
166 	loff_t start = iter->xarray_start + iter->iov_offset;  in collect_sample()
168 	size_t len, off, foff;  in collect_sample()  local
172 	last = (start + max - 1) / PAGE_SIZE;  in collect_sample()
174 		nr = xa_extract(iter->xarray, (void **)folios, index, last, ARRAY_SIZE(folios),  in collect_sample()
177 			return -EIO;  in collect_sample()
182 			foff = start - folio_pos(folio);  in collect_sample()
188 				len = min_t(size_t, max, PAGE_SIZE - off);  in collect_sample()
189 				len2 = min_t(size_t, len, SZ_2K);  in collect_sample()
197 				if (len2 < SZ_2K || s >= max - SZ_2K)  in collect_sample()
200 				max -= len;  in collect_sample()
201 				if (max <= 0)  in collect_sample()
204 				start += len;  in collect_sample()
215  * is_compressible() - Determines if a chunk of data is compressible.
225 	const size_t read_size = SZ_2K, bkt_size = 256, max = SZ_4M;  in is_compressible()  local
227 	size_t len;  in is_compressible()  local
232 	/* Preventive double check -- already checked in should_compress(). */  in is_compressible()
233 	len = iov_iter_count(data);  in is_compressible()
234 	if (unlikely(len < read_size))  in is_compressible()
237 	if (len - read_size > max)  in is_compressible()
238 		len = max;  in is_compressible()
240 	sample = kvzalloc(len, GFP_KERNEL);  in is_compressible()
248 	i = collect_sample(data, len, sample);  in is_compressible()
255 	len = i;  in is_compressible()
258 	if (has_repeated_data(sample, len))  in is_compressible()
269 	for (i = 0; i < len; i++)  in is_compressible()
278 	i = calc_byte_distribution(bkt, len);  in is_compressible()
285 	ret = has_low_entropy(bkt, len);  in is_compressible()
295 	const struct smb2_hdr *shdr = rq->rq_iov->iov_base;  in should_compress()
297 	if (unlikely(!tcon || !tcon->ses || !tcon->ses->server))  in should_compress()
300 	if (!tcon->ses->server->compression.enabled)  in should_compress()
303 	if (!(tcon->share_flags & SMB2_SHAREFLAG_COMPRESS_DATA))  in should_compress()
306 	if (shdr->Command == SMB2_WRITE) {  in should_compress()
307 		const struct smb2_write_req *wreq = rq->rq_iov->iov_base;  in should_compress()
309 		if (le32_to_cpu(wreq->Length) < SMB_COMPRESS_MIN_LEN)  in should_compress()
312 		return is_compressible(&rq->rq_iter);  in should_compress()
315 	return (shdr->Command == SMB2_READ);  in should_compress()
325 	if (!server || !rq || !rq->rq_iov || !rq->rq_iov->iov_base)  in smb_compress()
326 		return -EINVAL;  in smb_compress()
328 	if (rq->rq_iov->iov_len != sizeof(struct smb2_write_req))  in smb_compress()
329 		return -EINVAL;  in smb_compress()
331 	slen = iov_iter_count(&rq->rq_iter);  in smb_compress()
334 		ret = -ENOMEM;  in smb_compress()
339 	iter = rq->rq_iter;  in smb_compress()
342 		ret = -EIO;  in smb_compress()
353 		ret = -ENOMEM;  in smb_compress()
367 		hdr.Offset = cpu_to_le32(rq->rq_iov[0].iov_len);  in smb_compress()
371 		iov[1] = rq->rq_iov[0];  in smb_compress()
378 	} else if (ret == -EMSGSIZE || dlen >= slen) {  in smb_compress()