@@ -45,7 +45,7 @@ struct bucket {
};
/**
- * calc_shannon_entropy() - Compute Shannon entropy of the sampled data.
+ * has_low_entropy() - Compute Shannon entropy of the sampled data.
* @bkt: Bytes counts of the sample.
* @slen: Size of the sample.
*
@@ -60,7 +60,7 @@ struct bucket {
* 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 calc_shannon_entropy(struct bucket *bkt, size_t slen)
+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;
@@ -79,17 +79,21 @@ static bool calc_shannon_entropy(struct bucket *bkt, size_t 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:
- * 1: High probability (normal (Gaussian) distribution) of the data being compressible.
- * 0: A "hard no" for compression -- either a computed uniform distribution of the bytes (e.g.
- * random or encrypted data), or calc_shannon_entropy() returned false (see above).
- * 2: When computed byte distribution resulted in "low > n < high" grounds.
- * calc_shannon_entropy() should be used for a final decision.
+ * 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)
{
@@ -101,7 +105,7 @@ static int calc_byte_distribution(struct bucket *bkt, size_t slen)
sum += bkt[i].count;
if (sum > threshold)
- return i;
+ return BYTE_DIST_BAD;
for (; i < high && bkt[i].count > 0; i++) {
sum += bkt[i].count;
@@ -110,36 +114,29 @@ static int calc_byte_distribution(struct bucket *bkt, size_t slen)
}
if (i <= low)
- return 1;
+ return BYTE_DIST_GOOD;
if (i >= high)
- return 0;
+ return BYTE_DIST_BAD;
- return 2;
+ return BYTE_DIST_MAYBE;
}
-static bool check_ascii_bytes(const struct bucket *bkt)
+static bool is_mostly_ascii(const struct bucket *bkt)
{
- const size_t threshold = 64;
size_t count = 0;
int i;
- for (i = 0; i < threshold; i++)
+ for (i = 0; i < 256; i++)
if (bkt[i].count > 0)
- count++;
+ /* Too many non-ASCII (0-63) bytes. */
+ if (++count > 64)
+ return false;
- for (; i < 256; i++) {
- if (bkt[i].count > 0) {
- count++;
- if (count > threshold)
- break;
- }
- }
-
- return (count < threshold);
+ return true;
}
-static bool check_repeated_data(const u8 *sample, size_t len)
+static bool has_repeated_data(const u8 *sample, size_t len)
{
size_t s = len / 2;
@@ -222,71 +219,79 @@ static int collect_sample(const struct iov_iter *iter, ssize_t max, u8 *sample)
* is_compressible() - Determines if a chunk of data is compressible.
* @data: Iterator containing uncompressed data.
*
- * Return:
- * 0: @data is not compressible
- * 1: @data is compressible
- * -ENOMEM: failed to allocate memory for sample buffer
+ * 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 int is_compressible(const struct iov_iter *data)
+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;
- int i = 0, ret = 0;
size_t len;
u8 *sample;
+ bool ret = false;
+ int i;
+ /* Preventive double check -- already checked in should_compress(). */
len = iov_iter_count(data);
- if (len < read_size)
- return 0;
+ if (unlikely(len < read_size))
+ return ret;
if (len - read_size > max)
len = max;
sample = kvzalloc(len, GFP_KERNEL);
- if (!sample)
- return -ENOMEM;
+ if (!sample) {
+ WARN_ON_ONCE(1);
+
+ return ret;
+ }
/* Sample 2K bytes per page of the uncompressed data. */
- ret = collect_sample(data, len, sample);
- if (ret < 0)
+ i = collect_sample(data, len, sample);
+ if (i <= 0) {
+ WARN_ON_ONCE(1);
+
goto out;
+ }
- len = ret;
- ret = 1;
+ len = i;
+ ret = true;
- if (check_repeated_data(sample, len))
+ if (has_repeated_data(sample, len))
goto out;
bkt = kcalloc(bkt_size, sizeof(*bkt), GFP_KERNEL);
if (!bkt) {
- kvfree(sample);
- return -ENOMEM;
+ WARN_ON_ONCE(1);
+ ret = false;
+
+ goto out;
}
for (i = 0; i < len; i++)
bkt[sample[i]].count++;
- if (check_ascii_bytes(bkt))
+ if (is_mostly_ascii(bkt))
goto out;
/* Sort in descending order */
sort(bkt, bkt_size, sizeof(*bkt), cmp_bkt, NULL);
- ret = calc_byte_distribution(bkt, len);
- if (ret != 2)
+ i = calc_byte_distribution(bkt, len);
+ if (i != BYTE_DIST_MAYBE) {
+ ret = !!i;
+
goto out;
+ }
- ret = calc_shannon_entropy(bkt, len);
+ ret = has_low_entropy(bkt, len);
out:
kvfree(sample);
kfree(bkt);
- WARN(ret < 0, "%s: ret=%d\n", __func__, ret);
-
- return !!ret;
+ return ret;
}
bool should_compress(const struct cifs_tcon *tcon, const struct smb_rqst *rq)
@@ -305,7 +310,7 @@ bool should_compress(const struct cifs_tcon *tcon, const struct smb_rqst *rq)
if (shdr->Command == SMB2_WRITE) {
const struct smb2_write_req *wreq = rq->rq_iov->iov_base;
- if (wreq->Length < SMB_COMPRESS_MIN_LEN)
+ if (le32_to_cpu(wreq->Length) < SMB_COMPRESS_MIN_LEN)
return false;
return is_compressible(&rq->rq_iter);
Change is_compressible() return type to bool, use WARN_ON_ONCE(1) for internal errors and return false for those. Renames: check_repeated_data -> has_repeated_data check_ascii_bytes -> is_mostly_ascii (also refactor into a single loop) calc_shannon_entropy -> has_low_entropy Also wraps "wreq->Length" in le32_to_cpu() in should_compress() (caught by sparse). Signed-off-by: Enzo Matsumiya <ematsumiya@suse.de> Reported-by: Dan Carpenter <dan.carpenter@linaro.org> --- fs/smb/client/compress.c | 105 ++++++++++++++++++++------------------- 1 file changed, 55 insertions(+), 50 deletions(-)