Add dhcp_snprintf() for extracting DHCP string options.

diff --git a/src/include/gpxe/dhcp.h b/src/include/gpxe/dhcp.h
index 51fd819..5f1943e 100644 (file)
--- a/src/include/gpxe/dhcp.h
+++ b/src/include/gpxe/dhcp.h
@@ -160,6 +160,13 @@
  */
 #define DHCP_EB_SIADDR DHCP_ENCAP_OPT ( DHCP_EB_ENCAP, 3 )
 
+/** BIOS drive number
+ *
+ * This is the drive number for a drive emulated via INT 13.  0x80 is
+ * the first hard disk, 0x81 is the second hard disk, etc.
+ */
+#define DHCP_EB_BIOS_DRIVE DHCP_ENCAP_OPT ( DHCP_EB_ENCAP, 0xbd )
+
 /** Maximum normal DHCP option */
 #define DHCP_MAX_OPTION 254
 
@@ -255,6 +262,7 @@ struct dhcp_option {
                uint32_t dword;
                struct in_addr in;
                uint8_t bytes[0];
+               char string[0];
        } data;
 } __attribute__ (( packed ));
 
@@ -435,6 +443,8 @@ struct dhcp_session {
 extern unsigned long dhcp_num_option ( struct dhcp_option *option );
 extern void dhcp_ipv4_option ( struct dhcp_option *option,
                               struct in_addr *inp );
+extern int dhcp_snprintf ( char *buf, size_t size,
+                          struct dhcp_option *option );
 extern struct dhcp_option *
 find_dhcp_option ( struct dhcp_option_block *options, unsigned int tag );
 extern void register_dhcp_options ( struct dhcp_option_block *options );

diff --git a/src/net/dhcpopts.c b/src/net/dhcpopts.c
index ebd6de7..c906b19 100644 (file)
--- a/src/net/dhcpopts.c
+++ b/src/net/dhcpopts.c
@@ -101,6 +101,40 @@ void dhcp_ipv4_option ( struct dhcp_option *option, struct in_addr *inp ) {
                *inp = option->data.in;
 }
 
+/**
+ * Print DHCP string option value into buffer
+ *
+ * @v buf              Buffer into which to write the string
+ * @v size             Size of buffer
+ * @v option           DHCP option, or NULL
+ * @ret len            Length of formatted string
+ *
+ * DHCP option strings are stored without a NUL terminator.  This
+ * function provides a convenient way to extract these DHCP strings
+ * into standard C strings.  It is permitted to call dhcp_snprintf()
+ * with @c option set to NULL; in this case the buffer will be filled
+ * with an empty string.
+ *
+ * The usual snprintf() semantics apply with regard to buffer size,
+ * return value when the buffer is too small, etc.
+ */
+int dhcp_snprintf ( char *buf, size_t size, struct dhcp_option *option ) {
+       size_t len;
+       char *content = "";
+
+       if ( option ) {
+               /* Shrink buffer size so that it is only just large
+                * enough to contain the option data.  snprintf() will
+                * take care of everything else (inserting the NUL etc.)
+                */
+               len = ( option->len + 1 );
+               if ( len < size )
+                       size = len;
+               content = option->data.string;
+       }
+       return snprintf ( buf, size, "%s", content );
+}
+
 /**
  * Calculate length of a normal DHCP option
  *