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Re: [Qemu-devel] [PATCH v14 10/13] Add xbzrle_encode_buffer and xbzrle_d
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH v14 10/13] Add xbzrle_encode_buffer and xbzrle_decode_buffer functions |
Date: |
Tue, 03 Jul 2012 18:20:22 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120615 Thunderbird/13.0.1 |
On 07/03/2012 03:39 PM, Eric Blake wrote:
> On 07/03/2012 03:32 PM, Eric Blake wrote:
>
>>> + ret = uleb128_decode_small(src + i, &count);
>>> + if (ret < 0) {
>>
>> An nzrun should be a non-zero value; I'd write this as (ret <= 0) to
>> rule out an attempt to pass a zero-length nzrun.
>
> Correcting myself,
>
> if (ret < 0 || !count) {
>
> At this point, I think I will just bite the bullet and post a version of
> this code that incorporates my review.
Something like this (lightly tested):
/*
page = zrun nzrun
| zrun nzrun page
zrun = length
nzrun = length byte...
length = uleb128 encoded integer
*/
int xbzrle_encode_buffer(uint8_t *old_buf, uint8_t *new_buf, int slen,
uint8_t *dst, int dlen)
{
uint32_t zrun_len = 0, nzrun_len = 0;
int d = 0, i = 0;
long res, xor;
uint8_t *nzrun_start = NULL;
g_assert(!(((uintptr_t)old_buf | (uintptr_t)new_buf | slen) %
sizeof(long)));
while (i < slen) {
/* overflow */
if (d + 2 > dlen) {
return -1;
}
/* not aligned to sizeof(long) */
res = (slen - i) % sizeof(long);
while (res && old_buf[i] == new_buf[i]) {
zrun_len++;
i++;
res--;
}
if (!res) {
while (i < slen &&
(*(long *)(old_buf + i)) == (*(long *)(new_buf + i))) {
i += sizeof(long);
zrun_len += sizeof(long);
}
/* go over the rest */
while (i < slen && old_buf[i] == new_buf[i]) {
zrun_len++;
i++;
}
}
/* buffer unchanged */
if (zrun_len == slen) {
return 0;
}
/* skip last zero run */
if (i == slen) {
return d;
}
d += uleb128_encode_small(dst + d, zrun_len);
zrun_len = 0;
nzrun_start = new_buf + i;
/* overflow */
if (d + 2 > dlen) {
return -1;
}
/* not aligned to sizeof(long) */
res = (slen - i) % sizeof(long);
while (res && old_buf[i] != new_buf[i]) {
nzrun_len++;
i++;
res--;
}
if (!res) {
/* truncation to 32-bit long okay */
long mask = 0x0101010101010101ULL;
while (i < slen) {
xor = *(long *)(old_buf + i) ^ *(long *)(new_buf + i);
if ((xor - mask) & ~xor & (mask << 7)) {
/* found the end of an nzrun within the current long */
while (old_buf[i] != new_buf[i]) {
nzrun_len++;
i++;
}
break;
} else {
i += sizeof(long);
nzrun_len += sizeof(long);
}
}
}
d += uleb128_encode_small(dst + d, nzrun_len);
/* overflow */
if (d + nzrun_len > dlen) {
return -1;
}
memcpy(dst + d, nzrun_start, nzrun_len);
d += nzrun_len;
nzrun_len = 0;
}
return d;
}
int xbzrle_decode_buffer(uint8_t *src, int slen, uint8_t *dst, int dlen)
{
int i = 0, d = 0;
int ret;
uint32_t count = 0;
while (i < slen) {
/* zrun */
if (slen - i < 2) {
return -1;
}
ret = uleb128_decode_small(src + i, &count);
if (ret < 0 || (i && !count)) {
return -1;
}
i += ret;
d += count;
/* overflow */
if (d > dlen) {
return -1;
}
/* nzrun */
if (slen - i < 2) {
return -1;
}
ret = uleb128_decode_small(src + i, &count);
if (ret < 0 || !count) {
return -1;
}
i += ret;
/* overflow */
if (d + count > dlen || i + count > slen) {
return -1;
}
memcpy(dst + d , src + i, count);
d += count;
i += count;
}
return d;
}
--
Eric Blake address@hidden +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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[Qemu-devel] [PATCH v14 05/13] Add uleb encoding/decoding functions, Orit Wasserman, 2012/07/03
[Qemu-devel] [PATCH v14 11/13] Add XBZRLE to ram_save_block and ram_save_live, Orit Wasserman, 2012/07/03
[Qemu-devel] [PATCH v14 02/13] Add migration capabilities, Orit Wasserman, 2012/07/03
[Qemu-devel] [PATCH v14 13/13] Add XBZRLE statistics, Orit Wasserman, 2012/07/03