New upstream version 0.99.7.1

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+.\"     Title: pam_conv
+.\"    Author: 
+.\" Generator: DocBook XSL Stylesheets v1.70.1 <http://docbook.sf.net/>
+.\"      Date: 06/27/2006
+.\"    Manual: Linux\-PAM Manual
+.\"    Source: Linux\-PAM Manual
+.\"
+.TH "PAM_CONV" "3" "06/27/2006" "Linux\-PAM Manual" "Linux\-PAM Manual"
+.\" disable hyphenation
+.nh
+.\" disable justification (adjust text to left margin only)
+.ad l
+.SH "NAME"
+pam_conv \- PAM conversation function
+.SH "SYNOPSIS"
+.sp
+.ft B
+.nf
+#include <security/pam_appl.h>
+.fi
+.ft
+.sp
+.RS 3n
+.nf
+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;
+};
+    
+.fi
+.RE
+.SH "DESCRIPTION"
+.PP
+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
+\fIstruct pam_conv\fR
+passed to
+\fBpam_start\fR(3)
+at the start of the transaction.
+.PP
+When a module calls the referenced conv() function, the argument
+\fIappdata_ptr\fR
+is set to the second element of this structure.
+.PP
+The other arguments of a call to conv() concern the information exchanged by module and application. That is to say,
+\fInum_msg\fR
+holds the length of the array of pointers,
+\fImsg\fR. After a successful return, the pointer
+\fIresp\fR
+points to an array of pam_response structures, holding the application supplied text. The
+\fIresp_retcode\fR
+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
+\fBfree\fR(3). Note,
+\fI*resp\fR
+is a
+\fIstruct pam_response\fR
+array and not an array of pointers.
+.PP
+The number of responses is always equal to the
+\fInum_msg\fR
+conversation function argument. This does require that the response array is
+\fBfree\fR(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.
+.PP
+On failure, the conversation function should release any resources it has allocated, and return one of the predefined PAM error codes.
+.PP
+Each message can have one of four types, specified by the
+\fImsg_style\fR
+member of
+\fIstruct pam_message\fR:
+.TP 3n
+PAM_PROMPT_ECHO_OFF
+Obtain a string without echoing any text.
+.TP 3n
+PAM_PROMPT_ECHO_ON
+Obtain a string whilst echoing text.
+.TP 3n
+PAM_ERROR_MSG
+Display an error message.
+.TP 3n
+PAM_TEXT_INFO
+Display some text.
+.PP
+The point of having an array of messages is that it becomes possible to pass a number of things to the application in a single call from the module. It can also be convenient for the application that related things come at once: a windows based application can then present a single form with many messages/prompts on at once.
+.PP
+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_meg read only 'struct pam_message' pointers. Solaris' PAM implementation interprets this argument as a pointer to a pointer to an array of num_meg 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.
+.PP
+For what its worth the two known module writer work\-arounds for trying to maintain source level compatibility with both PAM implementations are:
+.TP 3n
+\(bu
+never call the conversation function with num_msg greater than one.
+.TP 3n
+\(bu
+set up msg as doubly referenced so both types of conversation function can find the messages. That is, make
+.sp
+.RS 3n
+.nf
+       msg[n] = & (( *msg )[n])
+       
+.fi
+.RE
+.SH "RETURN VALUES"
+.TP 3n
+PAM_BUF_ERR
+Memory buffer error.
+.TP 3n
+PAM_CONV_ERR
+Conversation failure. The application should not set
+\fI*resp\fR.
+.TP 3n
+PAM_SUCCESS
+Success.
+.SH "SEE ALSO"
+.PP
+
+\fBpam_start\fR(3),
+\fBpam_set_item\fR(3),
+\fBpam_get_item\fR(3),
+\fBpam_strerror\fR(3),
+\fBpam\fR(8)