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    Command:

    pam_conv

    
    
    

    SYNOPSIS

           #include <security/pam_appl.h>
    
           struct pam_message {
               int msg_style;
               const char *msg;
           };
    
           struct pam_response {
               char *resp;
               int resp_retcode;
           };
    
           struct pam_conv {
               int (*conv)(int num_msg, const struct pam_message **msg,
                           struct pam_response **resp, void *appdata_ptr);
               void *appdata_ptr;
           };
    
    
    

    DESCRIPTION

           The PAM library uses an application-defined callback to allow a direct
           communication between a loaded module and the application. This
           callback is specified by the struct pam_conv passed to pam_start(3) at
           the start of the transaction.
    
           When a module calls the referenced conv() function, the argument
           appdata_ptr is set to the second element of this structure.
    
           The other arguments of a call to conv() concern the information
           exchanged by module and application. That is to say, num_msg holds the
           length of the array of pointers, msg. After a successful return, the
           pointer resp points to an array of pam_response structures, holding the
           application supplied text. The resp_retcode member of this struct is
           unused and should be set to zero. It is the caller?s responsibility to
           release both, this array and the responses themselves, using free(3).
           Note, *resp is a struct pam_response array and not an array of
           pointers.
    
           The number of responses is always equal to the num_msg conversation
           function argument. This does require that the response array is
           free(3)?d after every call to the conversation function. The index of
           the responses corresponds directly to the prompt index in the
           pam_message array.
    
           On failure, the conversation function should release any resources it
           has allocated, and return one of the predefined PAM error codes.
    
           Each message can have one of four types, specified by the msg_style
           member of struct pam_message:
    
           PAM_PROMPT_ECHO_OFF
           things come at once: a windows based application can then present a
           single form with many messages/prompts on at once.
    
           In passing, it is worth noting that there is a descrepency between the
           way Linux-PAM handles the const struct pam_message **msg conversation
           function argument from the way that Solaris? PAM (and derivitives,
           known to include HP/UX, are there others?) does. Linux-PAM interprets
           the msg argument as entirely equivalent to the following prototype
           const struct pam_message *msg[] (which, in spirit, is consistent with
           the commonly used prototypes for argv argument to the familiar main()
           function: char **argv; and char *argv[]). Said another way Linux-PAM
           interprets the msg argument as a pointer to an array of num_msg read
           only ?struct pam_message? pointers. Solaris? PAM implementation
           interprets this argument as a pointer to a pointer to an array of
           num_msg pam_message structures. Fortunately, perhaps, for most
           module/application developers when num_msg has a value of one these two
           definitions are entirely equivalent. Unfortunately, casually raising
           this number to two has led to unanticipated compatibility problems.
    
           For what its worth the two known module writer work-arounds for trying
           to maintain source level compatibility with both PAM implementations
           are:
    
           ?   never call the conversation function with num_msg greater than one.
    
           ?   set up msg as doubly referenced so both types of conversation
               function can find the messages. That is, make
    
                          msg[n] = & (( *msg )[n])
    
    
    

    RETURN VALUES

           PAM_BUF_ERR
               Memory buffer error.
    
           PAM_CONV_ERR
               Conversation failure. The application should not set *resp.
    
           PAM_SUCCESS
               Success.
    
    
    

    SEE ALSO

           pam_start(3), pam_set_item(3), pam_get_item(3), pam_strerror(3), pam(8)
    
    
    

    Linux-PAM Manual 03/02/2009 PAM_CONV(3)

    
    
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