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net/netfilter/xt_repldata.h
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/* SPDX-License-Identifier: GPL-2.0 */
/*
* Today's hack: quantum tunneling in structs
*
* 'entries' and 'term' are never anywhere referenced by word in code. In fact,
* they serve as the hanging-off data accessed through repl.data[].
*/
/* tbl has the following structure equivalent, but is C99 compliant:
* struct {
* struct type##_replace repl;
* struct type##_standard entries[nhooks];
* struct type##_error term;
* } *tbl;
*/
#define xt_alloc_initial_table(type, typ2) ({ \
unsigned int hook_mask = info->valid_hooks; \
unsigned int nhooks = hweight32(hook_mask); \
unsigned int bytes = 0, hooknum = 0, i = 0; \
struct { \
struct type##_replace repl; \
struct type##_standard entries[]; \
} *tbl; \
struct type##_error *term; \
size_t term_offset = (offsetof(typeof(*tbl), entries[nhooks]) + \
__alignof__(*term) - 1) & ~(__alignof__(*term) - 1); \
tbl = kzalloc(term_offset + sizeof(*term), GFP_KERNEL); \
if (tbl == NULL) \
return NULL; \
term = (struct type##_error *)&(((char *)tbl)[term_offset]); \
strncpy(tbl->repl.name, info->name, sizeof(tbl->repl.name)); \
*term = (struct type##_error)typ2##_ERROR_INIT; \
tbl->repl.valid_hooks = hook_mask; \
tbl->repl.num_entries = nhooks + 1; \
tbl->repl.size = nhooks * sizeof(struct type##_standard) + \
sizeof(struct type##_error); \
for (; hook_mask != 0; hook_mask >>= 1, ++hooknum) { \
if (!(hook_mask & 1)) \
continue; \
tbl->repl.hook_entry[hooknum] = bytes; \
tbl->repl.underflow[hooknum] = bytes; \
tbl->entries[i++] = (struct type##_standard) \
typ2##_STANDARD_INIT(NF_ACCEPT); \
bytes += sizeof(struct type##_standard); \
} \
tbl; \
})
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