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<nss_action.h>: New abstraction for combining NSS modules and NSS actions

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nss_action manages a set of lists of actions; these are the portions
of the lines in nsswitch.conf to the right of the colons, like
"dns [!UNAVAIL=return] files".  Each permutation of actions and
conditionals is cached for reuse, which limits memory growth, and
refers to the static list of modules managed by nss_modules.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
This commit is contained in:
Florian Weimer
2020-02-20 09:32:27 +01:00
committed by DJ Delorie
parent 171689dac7
commit fd5b9b4458
4 changed files with 423 additions and 1 deletions
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108
nss/nss_action.h Normal file
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/* NSS actions, elements in a nsswitch.conf configuration line.
Copyright (c) 2020 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#ifndef _NSS_ACTION_H
#define _NSS_ACTION_H
#include <stddef.h>
/* See nss_database.h for a summary of how this relates. */
#include "nsswitch.h" /* For lookup_actions. */
struct nss_module;
/* A NSS action pairs a service module with the action for each result
state. */
struct nss_action
{
/* The service module that provides the functionality (potentially
not yet loaded). */
struct nss_module *module;
/* Action according to result. Two bits for each lookup_actions
value (from nsswitch.h), indexed by enum nss_status (from nss.h). */
unsigned int action_bits;
};
/* Value to add to first nss_status value to get zero. */
#define NSS_STATUS_BIAS 2
/* Number of bits per lookup action. */
#define NSS_BPL 2
#define NSS_BPL_MASK ((1 << NSS_BPL) - 1)
/* Index in actions of an NSS status. Note that in nss/nss.h the
status starts at -2, and we shift that up to zero by adding 2.
Thus for example NSS_STATUS_TRYAGAIN, which is -2, would index into
the 0th bit place as expected. */
static inline int
nss_actions_bits_index (enum nss_status status)
{
return NSS_BPL * (NSS_STATUS_BIAS + status);
}
/* Returns the lookup_action value for STATUS in ACTION. */
static inline lookup_actions
nss_action_get (const struct nss_action *action, enum nss_status status)
{
return ((action->action_bits >> nss_actions_bits_index (status))
& NSS_BPL_MASK);
}
/* Sets the lookup_action value for STATUS in ACTION. */
static inline void
nss_action_set (struct nss_action *action,
enum nss_status status, lookup_actions actions)
{
int offset = nss_actions_bits_index (status);
unsigned int mask = NSS_BPL_MASK << offset;
action->action_bits = ((action->action_bits & ~mask)
| ((unsigned int) actions << offset));
}
static inline void
nss_action_set_all (struct nss_action *action, lookup_actions actions)
{
unsigned int bits = actions & NSS_BPL_MASK;
action->action_bits = ( bits
| (bits << (NSS_BPL * 1))
| (bits << (NSS_BPL * 2))
| (bits << (NSS_BPL * 3))
| (bits << (NSS_BPL * 4))
);
}
/* A list of struct nss_action objects in array terminated by an
action with a NULL module. */
typedef struct nss_action *nss_action_list;
/* Returns a pointer to an allocated NSS action list that has COUNT
actions that matches the array at ACTIONS. */
nss_action_list __nss_action_allocate (struct nss_action *actions,
size_t count) attribute_hidden;
/* Returns a pointer to a list allocated by __nss_action_allocate, or
NULL on error. ENOMEM means a (temporary) memory allocation error,
EINVAL means that LINE is syntactically invalid. */
nss_action_list __nss_action_parse (const char *line);
/* Called from __libc_freeres. */
void __nss_action_freeres (void) attribute_hidden;
#endif /* _NSS_ACTION_H */