Adding a Service to Name Service Switch - c

Question

So I am trying to add a service to NSS (Name Service Switch). Please note the GNU guide on how to do it here. I have been following that guide. I need to implement a service that works with the passwd database.
The problem I am having is my module is not being called for certain functions. Let me reproduce some of my code here...
enum nss_status
_nss_myservice_setpwent (void) {
printf( "# %s\n", __FUNCTION__ ) ;
return NSS_STATUS_SUCCESS ;
} ;
enum nss_status
_nss_myservice_endpwent (void) {
printf( "# %s\n", __FUNCTION__ ) ;
return NSS_STATUS_SUCCESS ;
} ;
enum nss_status
_nss_myservice_getpwent_r (struct passwd *result, char *buffer,
size_t buflen, int *errnop) {
static int i = 0 ;
if( i++ == 0 ) {
printf( "# %s\n", __FUNCTION__ ) ;
return init_result( result, buffer, buflen, errnop ) ;
} else {
i = 0 ;
return NSS_STATUS_NOTFOUND ;
}
} ;
enum nss_status
_nss_myservice_getpwbynam (const char *nam, struct passwd *result, char *buffer,
size_t buflen, int *errnop) {
printf( "# %s with name %s\n", __FUNCTION__, nam ) ;
return init_result( result, buffer, buflen, errnop ) ;
} ;
enum nss_status
_nss_myservice_getpwbynam_r (const char *nam, struct passwd *result, char *buffer,
size_t buflen, int *errnop) {
printf( "# %s with name_r %s\n", __FUNCTION__, nam ) ;
return init_result( result, buffer, buflen, errnop ) ;
} ;
Init_result is an inline function that simply fills in the result with a dummy user no matter what the PARAMS are.
Now I have my /etc/nsswitch.conf setup as follows:
passwd: myservice compat
And for completeness here is my Makefile.
all:
gcc -fPIC -shared -o libnss_myservice.so.2 -Wl,-soname,libnss_myservice.so.2 myservice.c
install:
sudo install -m 0644 libnss_myservice.so.2 /lib
sudo /sbin/ldconfig -n /lib /usr/lib
clean:
/bin/rf -rf libnss_myservice.so.2
Now after installing this nss module I run getent on the command line and here is my output:
username#host:~/nss$ getent passwd
# _nss_myservice_setpwent
# _nss_myservice_getpwent_r
myuser:mypass:1:1:realname::
root:x:0:0:root:/root:/bin/bash
...
# _nss_myservice_endpwent
So as you can see that is working as I would expect. The iterative call is made which returns the user and then the compat service is called which returns all the user from /etc/passwd.
The problem is when I make this call, "getent passwd myuser", I get a return value of 2, "Key not found in database". This shows me my _nss_myservice_getpwbynam_r function is not being called. Any ideas why? I can provide the complete code if that would help.

Answer 1

You need to call the function _nss_myservice_getpwnam_r instead of _nss_myservice_getpwbynam_r.
After looking at ftp://ftp.acer-euro.com/gpl/Utility/glibc/glibc-2.2.5.tar/include/pwd.h :
#define DECLARE_NSS_PROTOTYPES(service) \
extern enum nss_status _nss_ ## service ## _setpwent (int); \
extern enum nss_status _nss_ ## service ## _endpwent (void); \
extern enum nss_status _nss_ ## service ## _getpwnam_r \ <<< this line
(const char *name, struct passwd *pwd, \
char *buffer, size_t buflen, int *errnop); \
extern enum nss_status _nss_ ## service ## _getpwuid_r \
(uid_t uid, struct passwd *pwd, \
char *buffer, size_t buflen, int *errnop); \
extern enum nss_status _nss_ ## service ##_getpwent_r \
(struct passwd *result, char *buffer, \
size_t buflen, int *errnop);