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/*-
* Copyright (c) 2014-2018 MongoDB, Inc.
* Copyright (c) 2008-2014 WiredTiger, Inc.
* All rights reserved.
*
* See the file LICENSE for redistribution information.
*/
#include "wt_internal.h"
/*
* __wt_modify_pack --
* Pack a modify structure into a buffer.
*/
int
__wt_modify_pack(WT_SESSION_IMPL *session,
WT_ITEM **modifyp, WT_MODIFY *entries, int nentries)
{
WT_ITEM *modify;
size_t len, *p;
uint8_t *data;
int i;
/*
* Build the in-memory modify value. It's the entries count, followed
* by the modify structure offsets written in order, followed by the
* data (data at the end to minimize unaligned reads/writes).
*/
len = sizeof(size_t); /* nentries */
for (i = 0; i < nentries; ++i) {
len += 3 * sizeof(size_t); /* WT_MODIFY fields */
len += entries[i].data.size; /* data */
}
WT_RET(__wt_scr_alloc(session, len, &modify));
data = (uint8_t *)modify->mem +
sizeof(size_t) + ((size_t)nentries * 3 * sizeof(size_t));
p = modify->mem;
*p++ = (size_t)nentries;
for (i = 0; i < nentries; ++i) {
*p++ = entries[i].data.size;
*p++ = entries[i].offset;
*p++ = entries[i].size;
memcpy(data, entries[i].data.data, entries[i].data.size);
data += entries[i].data.size;
}
modify->size = WT_PTRDIFF(data, modify->data);
*modifyp = modify;
return (0);
}
/*
* __modify_apply_one --
* Apply a single modify structure change to the buffer.
*/
static int
__modify_apply_one(WT_SESSION_IMPL *session, WT_CURSOR *cursor,
size_t data_size, size_t offset, size_t size, const uint8_t *data)
{
WT_ITEM *value;
size_t len;
uint8_t *from, *to;
bool sformat;
value = &cursor->value;
sformat = cursor->value_format[0] == 'S';
/*
* Grow the buffer to the maximum size we'll need. This is pessimistic
* because it ignores replacement bytes, but it's a simpler calculation.
*
* Grow the buffer before we fast-path the expected case. This function
* is often called using a cursor buffer referencing on-page memory and
* it's easy to overwrite a page. A side-effect of growing the buffer is
* to ensure the buffer's value is in buffer-local memory.
*
* Because the buffer may reference an overflow item, the data may not
* start at the start of the buffer's memory and we have to correct for
* that.
*/
len = WT_DATA_IN_ITEM(value) ? WT_PTRDIFF(value->data, value->mem) : 0;
WT_RET(__wt_buf_grow(session, value,
len + WT_MAX(value->size, offset) + data_size + (sformat ? 1 : 0)));
/*
* Fast-path the expected case, where we're overwriting a set of bytes
* that already exist in the buffer.
*/
if (value->size > offset + data_size && data_size == size) {
memmove((uint8_t *)value->data + offset, data, data_size);
return (0);
}
/*
* Decrement the size to discard the trailing nul (done after growing
* the buffer to ensure it can be restored without further checking).
*/
if (sformat)
--value->size;
/*
* If appending bytes past the end of the value, initialize gap bytes
* and copy the new bytes into place.
*/
if (value->size <= offset) {
if (value->size < offset)
memset((uint8_t *)value->data + value->size,
sformat ? ' ' : 0, offset - value->size);
memmove((uint8_t *)value->data + offset, data, data_size);
value->size = offset + data_size;
/* Restore the trailing nul. */
if (sformat)
((char *)value->data)[value->size++] = '\0';
return (0);
}
/*
* Correct the replacement size if it's nonsense, we can't replace more
* bytes than remain in the value. (Nonsense sizes are permitted in the
* API because we don't want to handle the errors.)
*/
if (value->size < offset + size)
size = value->size - offset;
if (data_size == size) { /* Overwrite */
/* Copy in the new data. */
memmove((uint8_t *)value->data + offset, data, data_size);
/*
* The new data must overlap the buffer's end (else, we'd use
* the fast-path code above). Set the buffer size to include
* the new data.
*/
value->size = offset + data_size;
} else { /* Shrink or grow */
/* Move trailing data forward/backward to its new location. */
from = (uint8_t *)value->data + (offset + size);
WT_ASSERT(session, WT_DATA_IN_ITEM(value) &&
from + (value->size - (offset + size)) <=
(uint8_t *)value->mem + value->memsize);
to = (uint8_t *)value->data + (offset + data_size);
WT_ASSERT(session, WT_DATA_IN_ITEM(value) &&
to + (value->size - (offset + size)) <=
(uint8_t *)value->mem + value->memsize);
memmove(to, from, value->size - (offset + size));
/* Copy in the new data. */
memmove((uint8_t *)value->data + offset, data, data_size);
/*
* Correct the size. This works because of how the C standard
* defines unsigned arithmetic, and gcc7 complains about more
* verbose forms:
*
* if (data_size > size)
* value->size += (data_size - size);
* else
* value->size -= (size - data_size);
*
* because the branches are identical.
*/
value->size += (data_size - size);
}
/* Restore the trailing nul. */
if (sformat)
((char *)value->data)[value->size++] = '\0';
return (0);
}
/*
* __wt_modify_apply_api --
* Apply a single set of WT_MODIFY changes to a buffer, the cursor API
* interface.
*/
int
__wt_modify_apply_api(WT_SESSION_IMPL *session,
WT_CURSOR *cursor, WT_MODIFY *entries, int nentries)
WT_GCC_FUNC_ATTRIBUTE((visibility("default")))
{
int i;
for (i = 0; i < nentries; ++i)
WT_RET(__modify_apply_one(session, cursor, entries[i].data.size,
entries[i].offset, entries[i].size, entries[i].data.data));
return (0);
}
/*
* __wt_modify_apply --
* Apply a single set of WT_MODIFY changes to a buffer.
*/
int
__wt_modify_apply(
WT_SESSION_IMPL *session, WT_CURSOR *cursor, const void *modify)
{
size_t data_size, nentries, offset, size;
const size_t *p;
const uint8_t *data;
/*
* Get the number of entries, and set a second pointer to reference the
* change data. The modify string isn't necessarily aligned for size_t
* access, copy to be sure.
*/
p = modify;
memcpy(&nentries, p++, sizeof(size_t));
data = (uint8_t *)modify +
sizeof(size_t) + (nentries * 3 * sizeof(size_t));
/* Step through the list of entries, applying them in order. */
for (; nentries-- > 0; data += data_size) {
memcpy(&data_size, p++, sizeof(size_t));
memcpy(&offset, p++, sizeof(size_t));
memcpy(&size, p++, sizeof(size_t));
WT_RET(__modify_apply_one(
session, cursor, data_size, offset, size, data));
}
return (0);
}
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