// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright (C) 2024, SUSE LLC
*
* Authors: Enzo Matsumiya <[email protected]>
*
* This file implements I/O compression support for SMB2 messages (SMB 3.1.1 only).
* See compress/ for implementation details of each algorithm.
*
* References:
* MS-SMB2 "3.1.4.4 Compressing the Message"
* MS-SMB2 "3.1.5.3 Decompressing the Chained Message"
* MS-XCA - for details of the supported algorithms
*/
#include <linux/slab.h>
#include <linux/kernel.h>
#include <linux/uio.h>
#include <linux/sort.h>
#include "cifsglob.h"
#include "../common/smb2pdu.h"
#include "cifsproto.h"
#include "smb2proto.h"
#include "compress/lz77.h"
#include "compress.h"
/*
* The heuristic_*() functions below try to determine data compressibility.
*
* Derived from fs/btrfs/compression.c, changing coding style, some parameters, and removing
* unused parts.
*
* Read that file for better and more detailed explanation of the calculations.
*
* The algorithms are ran in a collected sample of the input (uncompressed) data.
* The sample is formed of 2K reads in PAGE_SIZE intervals, with a maximum size of 4M.
*
* Parsing the sample goes from "low-hanging fruits" (fastest algorithms, likely compressible)
* to "need more analysis" (likely uncompressible).
*/
struct bucket {
unsigned int count;
};
/**
* has_low_entropy() - Compute Shannon entropy of the sampled data.
* @bkt: Bytes counts of the sample.
* @slen: Size of the sample.
*
* Return: true if the level (percentage of number of bits that would be required to
* compress the data) is below the minimum threshold.
*
* Note:
* There _is_ an entropy level here that's > 65 (minimum threshold) that would indicate a
* possibility of compression, but compressing, or even further analysing, it would waste so much
* resources that it's simply not worth it.
*
* Also Shannon entropy is the last computed heuristic; if we got this far and ended up
* with uncertainty, just stay on the safe side and call it uncompressible.
*/
static bool has_low_entropy(struct bucket *bkt, size_t slen)
{
const size_t threshold = 65, max_entropy = 8 * ilog2(16);
size_t i, p, p2, len, sum = 0;
#define pow4(n) (n * n * n * n)
len = ilog2(pow4(slen));
for (i = 0; i < 256 && bkt[i].count > 0; i++) {
p = bkt[i].count;
p2 = ilog2(pow4(p));
sum += p * (len - p2);
}
sum /= slen;
return ((sum * 100 / max_entropy) <= threshold);
}
#define BYTE_DIST_BAD 0
#define BYTE_DIST_GOOD 1
#define BYTE_DIST_MAYBE 2
/**
* calc_byte_distribution() - Compute byte distribution on the sampled data.
* @bkt: Byte counts of the sample.
* @slen: Size of the sample.
*
* Return:
* BYTE_DIST_BAD: A "hard no" for compression -- a computed uniform distribution of
* the bytes (e.g. random or encrypted data).
* BYTE_DIST_GOOD: High probability (normal (Gaussian) distribution) of the data being
* compressible.
* BYTE_DIST_MAYBE: When computed byte distribution resulted in "low > n < high"
* grounds. has_low_entropy() should be used for a final decision.
*/
static int calc_byte_distribution(struct bucket *bkt, size_t slen)
{
const size_t low = 64, high = 200, threshold = slen * 90 / 100;
size_t sum = 0;
int i;
for (i = 0; i < low; i++)
sum += bkt[i].count;
if (sum > threshold)
return BYTE_DIST_BAD;
for (; i < high && bkt[i].count > 0; i++) {
sum += bkt[i].count;
if (sum > threshold)
break;
}
if (i <= low)
return BYTE_DIST_GOOD;
if (i >= high)
return BYTE_DIST_BAD;
return BYTE_DIST_MAYBE;
}
static bool is_mostly_ascii(const struct bucket *bkt)
{
size_t count = 0;
int i;
for (i = 0; i < 256; i++)
if (bkt[i].count > 0)
/* Too many non-ASCII (0-63) bytes. */
if (++count > 64)
return false;
return true;
}
static bool has_repeated_data(const u8 *sample, size_t len)
{
size_t s = len / 2;
return (!memcmp(&sample[0], &sample[s], s));
}
static int cmp_bkt(const void *_a, const void *_b)
{
const struct bucket *a = _a, *b = _b;
/* Reverse sort. */
if (a->count > b->count)
return -1;
return 1;
}
/*
* TODO:
* Support other iter types, if required.
* Only ITER_XARRAY is supported for now.
*/
static int collect_sample(const struct iov_iter *iter, ssize_t max, u8 *sample)
{
struct folio *folios[16], *folio;
unsigned int nr, i, j, npages;
loff_t start = iter->xarray_start + iter->iov_offset;
pgoff_t last, index = start / PAGE_SIZE;
size_t len, off, foff;
ssize_t ret = 0;
void *p;
int s = 0;
last = (start + max - 1) / PAGE_SIZE;
do {
nr = xa_extract(iter->xarray, (void **)folios, index, last, ARRAY_SIZE(folios),
XA_PRESENT);
if (nr == 0)
return -EIO;
for (i = 0; i < nr; i++) {
folio = folios[i];
npages = folio_nr_pages(folio);
foff = start - folio_pos(folio);
off = foff % PAGE_SIZE;
for (j = foff / PAGE_SIZE; j < npages; j++) {
size_t len2;
len = min_t(size_t, max, PAGE_SIZE - off);
len2 = min_t(size_t, len, SZ_2K);
p = kmap_local_page(folio_page(folio, j));
memcpy(&sample[s], p, len2);
kunmap_local(p);
if (ret < 0)
return ret;
s += len2;
if (len2 < SZ_2K || s >= max - SZ_2K)
return s;
max -= len;
if (max <= 0)
return s;
start += len;
off = 0;
index++;
}
}
} while (nr == ARRAY_SIZE(folios));
return s;
}
/**
* is_compressible() - Determines if a chunk of data is compressible.
* @data: Iterator containing uncompressed data.
*
* Return: true if @data is compressible, false otherwise.
*
* Tests shows that this function is quite reliable in predicting data compressibility,
* matching close to 1:1 with the behaviour of LZ77 compression success and failures.
*/
static bool is_compressible(const struct iov_iter *data)
{
const size_t read_size = SZ_2K, bkt_size = 256, max = SZ_4M;
struct bucket *bkt = NULL;
size_t len;
u8 *sample;
bool ret = false;
int i;
/* Preventive double check -- already checked in should_compress(). */
len = iov_iter_count(data);
if (unlikely(len < read_size))
return ret;
if (len - read_size > max)
len = max;
sample = kvzalloc(len, GFP_KERNEL);
if (!sample) {
WARN_ON_ONCE(1);
return ret;
}
/* Sample 2K bytes per page of the uncompressed data. */
i = collect_sample(data, len, sample);
if (i <= 0) {
WARN_ON_ONCE(1);
goto out;
}
len = i;
ret = true;
if (has_repeated_data(sample, len))
goto out;
bkt = kcalloc(bkt_size, sizeof(*bkt), GFP_KERNEL);
if (!bkt) {
WARN_ON_ONCE(1);
ret = false;
goto out;
}
for (i = 0; i < len; i++)
bkt[sample[i]].count++;
if (is_mostly_ascii(bkt))
goto out;
/* Sort in descending order */
sort(bkt, bkt_size, sizeof(*bkt), cmp_bkt, NULL);
i = calc_byte_distribution(bkt, len);
if (i != BYTE_DIST_MAYBE) {
ret = !!i;
goto out;
}
ret = has_low_entropy(bkt, len);
out:
kvfree(sample);
kfree(bkt);
return ret;
}
bool should_compress(const struct cifs_tcon *tcon, const struct smb_rqst *rq)
{
const struct smb2_hdr *shdr = rq->rq_iov->iov_base;
if (unlikely(!tcon || !tcon->ses || !tcon->ses->server))
return false;
if (!tcon->ses->server->compression.enabled)
return false;
if (!(tcon->share_flags & SMB2_SHAREFLAG_COMPRESS_DATA))
return false;
if (shdr->Command == SMB2_WRITE) {
const struct smb2_write_req *wreq = rq->rq_iov->iov_base;
if (le32_to_cpu(wreq->Length) < SMB_COMPRESS_MIN_LEN)
return false;
return is_compressible(&rq->rq_iter);
}
return (shdr->Command == SMB2_READ);
}
int smb_compress(struct TCP_Server_Info *server, struct smb_rqst *rq, compress_send_fn send_fn)
{
struct iov_iter iter;
u32 slen, dlen;
void *src, *dst = NULL;
int ret;
if (!server || !rq || !rq->rq_iov || !rq->rq_iov->iov_base)
return -EINVAL;
if (rq->rq_iov->iov_len != sizeof(struct smb2_write_req))
return -EINVAL;
slen = iov_iter_count(&rq->rq_iter);
src = kvzalloc(slen, GFP_KERNEL);
if (!src) {
ret = -ENOMEM;
goto err_free;
}
/* Keep the original iter intact. */
iter = rq->rq_iter;
if (!copy_from_iter_full(src, slen, &iter)) {
ret = -EIO;
goto err_free;
}
/*
* This is just overprovisioning, as the algorithm will error out if @dst reaches 7/8
* of @slen.
*/
dlen = slen;
dst = kvzalloc(dlen, GFP_KERNEL);
if (!dst) {
ret = -ENOMEM;
goto err_free;
}
ret = lz77_compress(src, slen, dst, &dlen);
if (!ret) {
struct smb2_compression_hdr hdr = { 0 };
struct smb_rqst comp_rq = { .rq_nvec = 3, };
struct kvec iov[3];
hdr.ProtocolId = SMB2_COMPRESSION_TRANSFORM_ID;
hdr.OriginalCompressedSegmentSize = cpu_to_le32(slen);
hdr.CompressionAlgorithm = SMB3_COMPRESS_LZ77;
hdr.Flags = SMB2_COMPRESSION_FLAG_NONE;
hdr.Offset = cpu_to_le32(rq->rq_iov[0].iov_len);
iov[0].iov_base = &hdr;
iov[0].iov_len = sizeof(hdr);
iov[1] = rq->rq_iov[0];
iov[2].iov_base = dst;
iov[2].iov_len = dlen;
comp_rq.rq_iov = iov;
ret = send_fn(server, 1, &comp_rq);
} else if (ret == -EMSGSIZE || dlen >= slen) {
ret = send_fn(server, 1, rq);
}
err_free:
kvfree(dst);
kvfree(src);
return ret;
}
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