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pid1: use a cache for all unit aliases

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This reworks how we load units from disk. Instead of chasing symlinks every
time we are asked to load a unit by name, we slurp all symlinks from disk
and build two hashmaps:
1. from unit name to either alias target, or fragment on disk
   (if an alias, we put just the target name in the hashmap, if a fragment
    we put an absolute path, so we can distinguish both).
2. from a unit name to all aliases

Reading all this data can be pretty costly (40 ms) on my machine, so we keep it
around for reuse.

The advantage is that we can reliably know what all the aliases of a given unit
are. This means we can reliably load dropins under all names. This fixes #11972.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek
2019-07-30 14:01:46 +02:00
parent 7d1e91d1a9
commit e8630e6952
9 changed files with 532 additions and 390 deletions
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src/shared/unit-file.c
+353
View File
@@ -1,7 +1,14 @@
/* SPDX-License-Identifier: LGPL-2.1+ */
#include "dirent-util.h"
#include "fd-util.h"
#include "fs-util.h"
#include "macro.h"
#include "path-lookup.h"
#include "set.h"
#include "stat-util.h"
#include "string-util.h"
#include "strv.h"
#include "unit-file.h"
bool unit_type_may_alias(UnitType type) {
@@ -94,3 +101,349 @@ int unit_validate_alias_symlink_and_warn(const char *filename, const char *targe
return 0;
}
#define FOLLOW_MAX 8
static int unit_ids_map_get(
Hashmap *unit_ids_map,
const char *unit_name,
const char **ret_fragment_path) {
/* Resolve recursively until we hit an absolute path, i.e. a non-aliased unit.
*
* We distinguish the case where unit_name was not found in the hashmap at all, and the case where
* some symlink was broken.
*
* If a symlink target points to an instance name, then we also check for the template. */
const char *id = NULL;
int r;
for (unsigned n = 0; n < FOLLOW_MAX; n++) {
const char *t = hashmap_get(unit_ids_map, id ?: unit_name);
if (!t) {
_cleanup_free_ char *template = NULL;
if (!id)
return -ENOENT;
r = unit_name_template(id, &template);
if (r == -EINVAL)
return -ENXIO; /* we failed to find the symlink target */
if (r < 0)
return log_error_errno(r, "Failed to determine template name for %s: %m", id);
t = hashmap_get(unit_ids_map, template);
if (!t)
return -ENXIO;
/* We successfully switched from instanced name to a template, let's continue */
}
if (path_is_absolute(t)) {
if (ret_fragment_path)
*ret_fragment_path = t;
return 0;
}
id = t;
}
return -ELOOP;
}
int unit_file_build_name_map(
const LookupPaths *lp,
Hashmap **ret_unit_ids_map,
Hashmap **ret_unit_names_map,
Set **ret_path_cache) {
/* Build two mappings: any name → main unit (i.e. the end result of symlink resolution), unit name →
* all aliases (i.e. the entry for a given key is a a list of all names which point to this key). The
* key is included in the value iff we saw a file or symlink with that name. In other words, if we
* have a key, but it is not present in the value for itself, there was an alias pointing to it, but
* the unit itself is not loadable.
*
* At the same, build a cache of paths where to find units.
*/
_cleanup_hashmap_free_ Hashmap *ids = NULL, *names = NULL;
_cleanup_set_free_free_ Set *paths = NULL;
char **dir;
int r;
if (ret_path_cache) {
paths = set_new(&path_hash_ops);
if (!paths)
return log_oom();
}
STRV_FOREACH(dir, (char**) lp->search_path) {
struct dirent *de;
_cleanup_closedir_ DIR *d = NULL;
d = opendir(*dir);
if (!d) {
if (errno != ENOENT)
log_warning_errno(errno, "Failed to open \"%s\", ignoring: %m", *dir);
continue;
}
FOREACH_DIRENT(de, d, log_warning_errno(errno, "Failed to read \"%s\", ignoring: %m", *dir)) {
char *filename;
_cleanup_free_ char *_filename_free = NULL, *simplified = NULL;
const char *suffix, *dst = NULL;
filename = path_join(*dir, de->d_name);
if (!filename)
return log_oom();
if (ret_path_cache) {
r = set_consume(paths, filename);
if (r < 0)
return log_oom();
/* We will still use filename below. This is safe because we know the set
* holds a reference. */
} else
_filename_free = filename; /* Make sure we free the filename. */
if (!unit_name_is_valid(de->d_name, UNIT_NAME_ANY))
continue;
assert_se(suffix = strrchr(de->d_name, '.'));
/* search_path is ordered by priority (highest first). If the name is already mapped
* to something (incl. itself), it means that we have already seen it, and we should
* ignore it here. */
if (hashmap_contains(ids, de->d_name))
continue;
if (de->d_type == DT_LNK) {
/* We don't explicitly check for alias loops here. unit_ids_map_get() which
* limits the number of hops should be used to access the map. */
_cleanup_free_ char *target = NULL, *target_abs = NULL;
r = readlinkat_malloc(dirfd(d), de->d_name, &target);
if (r < 0) {
log_warning_errno(r, "Failed to read symlink %s/%s, ignoring: %m",
*dir, de->d_name);
continue;
}
if (!path_is_absolute(target)) {
target_abs = path_join(*dir, target);
if (!target_abs)
return log_oom();
free_and_replace(target, target_abs);
}
/* Get rid of "." and ".." components in target path */
r = chase_symlinks(target, lp->root_dir, CHASE_NOFOLLOW | CHASE_NONEXISTENT, &simplified);
if (r < 0) {
log_warning_errno(r, "Failed to resolve symlink %s pointing to %s, ignoring: %m",
filename, target);
continue;
}
/* Check if the symlink goes outside of our search path.
* If yes, it's a linked unit file or mask, and we don't care about the target name.
* Let's just store the link destination directly.
* If not, let's verify that it's a good symlink. */
char *tail = path_startswith_strv(simplified, lp->search_path);
if (tail) {
bool self_alias;
dst = basename(simplified);
self_alias = streq(dst, de->d_name);
if (is_path(tail))
log_full(self_alias ? LOG_DEBUG : LOG_WARNING,
"Suspicious symlink %s→%s, treating as alias.",
filename, simplified);
r = unit_validate_alias_symlink_and_warn(filename, simplified);
if (r < 0)
continue;
if (self_alias) {
/* A self-alias that has no effect */
log_debug("%s: self-alias: %s/%s → %s, ignoring.",
__func__, *dir, de->d_name, dst);
continue;
}
log_debug("%s: alias: %s/%s → %s", __func__, *dir, de->d_name, dst);
} else {
dst = simplified;
log_debug("%s: linked unit file: %s/%s → %s", __func__, *dir, de->d_name, dst);
}
} else {
dst = filename;
log_debug("%s: normal unit file: %s", __func__, dst);
}
r = hashmap_put_strdup(&ids, de->d_name, dst);
if (r < 0)
return log_warning_errno(r, "Failed to add entry to hashmap (%s→%s): %m",
de->d_name, dst);
}
}
/* Let's also put the names in the reverse db. */
Iterator it;
const char *dummy, *src;
HASHMAP_FOREACH_KEY(dummy, src, ids, it) {
const char *dst;
r = unit_ids_map_get(ids, src, &dst);
if (r < 0)
continue;
if (null_or_empty_path(dst) != 0)
continue;
/* Do not treat instance symlinks that point to the template as aliases */
if (unit_name_is_valid(basename(dst), UNIT_NAME_TEMPLATE) &&
unit_name_is_valid(src, UNIT_NAME_INSTANCE))
continue;
r = string_strv_hashmap_put(&names, basename(dst), src);
if (r < 0)
return log_warning_errno(r, "Failed to add entry to hashmap (%s→%s): %m",
basename(dst), src);
}
*ret_unit_ids_map = TAKE_PTR(ids);
*ret_unit_names_map = TAKE_PTR(names);
if (ret_path_cache)
*ret_path_cache = TAKE_PTR(paths);
return 0;
}
int unit_file_find_fragment(
Hashmap *unit_ids_map,
Hashmap *unit_name_map,
const char *unit_name,
const char **ret_fragment_path,
Set **ret_names) {
const char *fragment = NULL;
_cleanup_free_ char *template = NULL, *instance = NULL;
_cleanup_set_free_free_ Set *names = NULL;
char **t, **nnn;
int r, name_type;
/* Finds a fragment path, and returns the set of names:
* if we have …/foo.service and …/foo-alias.service→foo.service,
* and …/foo@.service and …/foo-alias@.service→foo@.service,
* and …/foo@inst.service,
* this should return:
* foo.service → …/foo.service, {foo.service, foo-alias.service},
* foo-alias.service → …/foo.service, {foo.service, foo-alias.service},
* foo@.service → …/foo@.service, {foo@.service, foo-alias@.service},
* foo-alias@.service → …/foo@.service, {foo@.service, foo-alias@.service},
* foo@bar.service → …/foo@.service, {foo@bar.service, foo-alias@bar.service},
* foo-alias@bar.service → …/foo@.service, {foo@bar.service, foo-alias@bar.service},
* foo-alias@inst.service → …/foo@inst.service, {foo@inst.service, foo-alias@inst.service}.
*/
name_type = unit_name_to_instance(unit_name, &instance);
if (name_type < 0)
return name_type;
names = set_new(&string_hash_ops);
if (!names)
return -ENOMEM;
/* The unit always has its own name if it's not a template. */
if (unit_name_is_valid(unit_name, UNIT_NAME_PLAIN | UNIT_NAME_INSTANCE)) {
r = set_put_strdup(names, unit_name);
if (r < 0)
return r;
}
/* First try to load fragment under the original name */
r = unit_ids_map_get(unit_ids_map, unit_name, &fragment);
if (r < 0 && !IN_SET(r, -ENOENT, -ENXIO))
return log_debug_errno(r, "Cannot load unit %s: %m", unit_name);
if (fragment) {
/* Add any aliases of the original name to the set of names */
nnn = hashmap_get(unit_name_map, basename(fragment));
STRV_FOREACH(t, nnn) {
if (instance && unit_name_is_valid(*t, UNIT_NAME_TEMPLATE)) {
char *inst;
r = unit_name_replace_instance(*t, instance, &inst);
if (r < 0)
return log_debug_errno(r, "Cannot build instance name %s+%s: %m", *t, instance);
if (!streq(unit_name, inst))
log_debug("%s: %s has alias %s", __func__, unit_name, inst);
log_info("%s: %s+%s → %s", __func__, *t, instance, inst);
r = set_consume(names, inst);
} else {
if (!streq(unit_name, *t))
log_debug("%s: %s has alias %s", __func__, unit_name, *t);
r = set_put_strdup(names, *t);
}
if (r < 0)
return r;
}
}
if (!fragment && name_type == UNIT_NAME_INSTANCE) {
/* Look for a fragment under the template name */
r = unit_name_template(unit_name, &template);
if (r < 0)
return log_error_errno(r, "Failed to determine template name: %m");
r = unit_ids_map_get(unit_ids_map, template, &fragment);
if (r < 0 && !IN_SET(r, -ENOENT, -ENXIO))
return log_debug_errno(r, "Cannot load template %s: %m", *t);
if (fragment) {
/* Add any aliases of the original name to the set of names */
nnn = hashmap_get(unit_name_map, basename(fragment));
STRV_FOREACH(t, nnn) {
_cleanup_free_ char *inst = NULL;
const char *inst_fragment = NULL;
r = unit_name_replace_instance(*t, instance, &inst);
if (r < 0)
return log_debug_errno(r, "Cannot build instance name %s+%s: %m", template, instance);
/* Exclude any aliases that point in some other direction. */
r = unit_ids_map_get(unit_ids_map, inst, &inst_fragment);
if (r < 0 && !IN_SET(r, -ENOENT, -ENXIO))
return log_debug_errno(r, "Cannot find instance fragment %s: %m", inst);
if (inst_fragment &&
!streq(basename(inst_fragment), basename(fragment))) {
log_debug("Instance %s has fragment %s and is not an alias of %s.",
inst, inst_fragment, unit_name);
continue;
}
if (!streq(unit_name, inst))
log_info("%s: %s has alias %s", __func__, unit_name, inst);
r = set_consume(names, TAKE_PTR(inst));
if (r < 0)
return r;
}
}
}
*ret_fragment_path = fragment;
*ret_names = TAKE_PTR(names);
// FIXME: if instance, consider any unit names with different template name
return 0;
}
src/shared/unit-file.h
+15
View File
@@ -3,10 +3,12 @@
#include <stdbool.h>
#include "hashmap.h"
#include "unit-name.h"
typedef enum UnitFileState UnitFileState;
typedef enum UnitFileScope UnitFileScope;
typedef struct LookupPaths LookupPaths;
enum UnitFileState {
UNIT_FILE_ENABLED,
@@ -37,3 +39,16 @@ bool unit_type_may_alias(UnitType type) _const_;
bool unit_type_may_template(UnitType type) _const_;
int unit_validate_alias_symlink_and_warn(const char *filename, const char *target);
int unit_file_build_name_map(
const LookupPaths *lp,
Hashmap **ret_unit_ids_map,
Hashmap **ret_unit_names_map,
Set **ret_path_cache);
int unit_file_find_fragment(
Hashmap *unit_ids_map,
Hashmap *unit_name_map,
const char *unit_name,
const char **ret_fragment_path,
Set **names);