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sub[ug]id: compare range before comparing username/UID, to avoid unnecessary syscalls

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Change suggested by Nicolas François as performance optimization.
Performance penalty would be really noticeable when usernames are
stored in remote databases (ldap).

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
This commit is contained in:
Bostjan Skufca 2014-09-06 18:47:55 +00:00 committed by Serge Hallyn
parent 37e2a687e3
commit 1d049b6aed
1 changed files with 30 additions and 28 deletions
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58
lib/subordinateio.c
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@ -245,36 +245,38 @@ static const struct subordinate_range *find_range(struct commonio_db *db,
unsigned long first = range->start;
unsigned long last = first + range->count - 1;
/*
* First check if range owner is specified as numeric UID
* and if it matches.
*/
if (0 != strcmp(range->owner, owner_uid_string)) {
/*
* Ok, this range owner is not specified as numeric UID
* we are looking for. It may be specified as another
* UID or as a literal username.
*
* If specified as another UID, the call to getpwnam()
* will return NULL.
*
* If specified as literal username, we will get its
* UID and compare that to UID we are looking for.
*/
const struct passwd *range_owner_pwd;
range_owner_pwd = getpwnam(range->owner);
if (NULL == range_owner_pwd) {
continue;
}
if (owner_uid != range_owner_pwd->pw_uid) {
continue;
}
/* For performance reasons check range before using getpwnam() */
if ((val < first) || (val > last)) {
continue;
}
/* Owner matches, now let us check this UID/GID range */
if ((val >= first) && (val <= last)) {
/*
* Range matches. Check if range owner is specified
* as numeric UID and if it matches.
*/
if (0 == strcmp(range->owner, owner_uid_string)) {
return range;
}
/*
* Ok, this range owner is not specified as numeric UID
* we are looking for. It may be specified as another
* UID or as a literal username.
*
* If specified as another UID, the call to getpwnam()
* will return NULL.
*
* If specified as literal username, we will get its
* UID and compare that to UID we are looking for.
*/
const struct passwd *range_owner_pwd;
range_owner_pwd = getpwnam(range->owner);
if (NULL == range_owner_pwd) {
continue;
}
if (owner_uid == range_owner_pwd->pw_uid) {
return range;
}
}