[v3,4/8] libnet: Add functions for downloading and parsing pxelinux.cfg files

diff --git a/lib/libnet/Makefile b/lib/libnet/Makefile
index dfefea9..a2a6570 100644
--- a/lib/libnet/Makefile
+++ b/lib/libnet/Makefile
@@ -19,7 +19,7 @@  include $(TOP)/make.rules
 CFLAGS += -I. -I.. -I../libc/include -I$(TOP)/include $(FLAG)
 
 SRCS =	ethernet.c ipv4.c udp.c tcp.c dns.c bootp.c dhcp.c tftp.c \
-	ipv6.c dhcpv6.c icmpv6.c ndp.c netload.c ping.c args.c
+	ipv6.c dhcpv6.c icmpv6.c ndp.c netload.c ping.c args.c pxelinux.c
 
 OBJS = $(SRCS:%.c=%.o)
 
diff --git a/lib/libnet/pxelinux.c b/lib/libnet/pxelinux.c
new file mode 100644
index 0000000..d702811
--- /dev/null
+++ b/lib/libnet/pxelinux.c
@@ -0,0 +1,212 @@ 
+/*****************************************************************************
+ * pxelinux.cfg-style config file support.
+ *
+ * See https://www.syslinux.org/wiki/index.php?title=PXELINUX for information
+ * about the pxelinux config file layout.
+ *
+ * Copyright 2018 Red Hat, Inc.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the BSD License which accompanies this distribution, and is
+ * available at http://www.opensource.org/licenses/bsd-license.php
+ *
+ * Contributors:
+ *     Thomas Huth, Red Hat Inc. - initial implementation
+ *****************************************************************************/
+
+#include <stdio.h>
+#include <string.h>
+#include "tftp.h"
+#include "pxelinux.h"
+
+/**
+ * Call tftp() and report errors (excet "file-not-found" errors)
+ */
+static int pxelinux_tftp_load(filename_ip_t *fnip, void *buffer, int len,
+                              int retries)
+{
+	tftp_err_t tftp_err;
+	int rc, ecode;
+
+	rc = tftp(fnip, buffer, len, retries, &tftp_err);
+
+	if (rc > 0) {
+		printf("\r  TFTP: Received %s (%d bytes)\n",
+		       fnip->filename, rc);
+	} else if (rc == -3) {
+		/* Ignore file-not-found (since we are probing the files)
+		 * and simply erase the "Receiving data:  0 KBytes" string */
+		printf("\r                           \r");
+	} else {
+		const char *errstr = NULL;
+		rc = tftp_get_error_info(fnip, &tftp_err, rc, &errstr, &ecode);
+		if (errstr)
+			printf("\r  TFTP error: %s\n", errstr);
+	}
+
+	return rc;
+}
+
+/**
+ * Try to load a pxelinux.cfg file by probing the possible file names.
+ * Note that this function will overwrite filename_ip_t->filename.
+ */
+static int pxelinux_load_cfg(filename_ip_t *fn_ip, uint8_t *mac,
+                             int retries, char *cfgbuf, int cfgbufsize)
+{
+	int rc, idx;
+	char *baseptr;
+
+	/* Try to get a usable base directory from the DHCP bootfile name */
+	baseptr = strrchr(fn_ip->filename, '/');
+	if (!baseptr)
+		baseptr = fn_ip->filename;
+	else
+		++baseptr;
+	/* Check that we've got enough space to store "pxelinux.cfg/" and
+	 * the UUID (which is the longest file name) there */
+	if (baseptr - fn_ip->filename > sizeof(fn_ip->filename) - 50) {
+		puts("Error: The bootfile string is too long for deriving the "
+		     "pxelinux.cfg file name from it.");
+		return -1;
+	}
+	strcpy(baseptr, "pxelinux.cfg/");
+	baseptr += strlen(baseptr);
+
+	puts("Trying pxelinux.cfg files...");
+
+	/* Look for config file with MAC address in its name */
+	sprintf(baseptr, "01-%02x-%02x-%02x-%02x-%02x-%02x",
+		mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);
+	rc = pxelinux_tftp_load(fn_ip, cfgbuf, cfgbufsize - 1, retries);
+	if (rc > 0) {
+		return rc;
+	}
+
+	/* Look for config file with IP address in its name */
+	if (fn_ip->ip_version == 4) {
+		sprintf(baseptr, "%02X%02X%02X%02X",
+			(fn_ip->own_ip >> 24) & 0xff,
+			(fn_ip->own_ip >> 16) & 0xff,
+			(fn_ip->own_ip >> 8) & 0xff,
+			fn_ip->own_ip & 0xff);
+		for (idx = 0; idx <= 7; idx++) {
+			baseptr[8 - idx] = 0;
+			rc = pxelinux_tftp_load(fn_ip, cfgbuf, cfgbufsize - 1,
+			                        retries);
+			if (rc > 0) {
+				return rc;
+			}
+		}
+	}
+
+	/* Try "default" config file */
+	strcpy(baseptr, "default");
+	rc = pxelinux_tftp_load(fn_ip, cfgbuf, cfgbufsize - 1, retries);
+
+	return rc;
+}
+
+/**
+ * Parse a pxelinux-style configuration file.
+ * The discovered entries are filled into the "struct pl_cfg_entry entries[]"
+ * array. Note that the callers must keep the cfg buffer valid as long as
+ * they wish to access the "struct pl_cfg_entry" entries, since the pointers
+ * in entries point to the original location in the cfg buffer area. The cfg
+ * buffer is altered for this, too, e.g. terminating NUL-characters are put
+ * into the right locations.
+ * @param cfg          Pointer to the buffer with contents of the config file
+ * @param cfgsize      Size of the cfg buffer
+ * @param entries      Pointer to array where the results should be put into
+ * @param max_entries  Number of available slots in the entries array
+ * @param def_ent      Used to return the index of the default entry
+ * @return             Number of valid entries
+ */
+int pxelinux_parse_cfg(char *cfg, int cfgsize, struct pl_cfg_entry *entries,
+                       int max_entries, int *def_ent)
+{
+	int num_entries = 0;
+	char *ptr = cfg, *nextptr, *eol, *arg;
+	char *defaultlabel = NULL;
+
+	*def_ent = 0;
+
+	cfg[cfgsize - 1] = 0;  /* Make sure it is NUL-terminated */
+
+	while (ptr < cfg + cfgsize && num_entries < max_entries) {
+		eol = strchr(ptr, '\n');
+		if (!eol) {
+			eol = cfg + cfgsize;
+		}
+		nextptr = eol + 1;
+		do {
+			*eol-- = '\0';	/* Remove spaces, tabs and returns */
+		} while (eol >= ptr &&
+		         (*eol == '\r' || *eol == ' ' || *eol == '\t'));
+		while (*ptr == ' ' || *ptr == '\t') {
+			ptr++;
+		}
+		if (*ptr == 0 || *ptr == '#') {
+			goto nextline;	/* Ignore comments and empty lines */
+		}
+		arg = strchr(ptr, ' ');	/* Search space between cmnd and arg */
+		if (!arg) {
+			arg = strchr(ptr, '\t');
+		}
+		if (!arg) {
+			printf("Failed to parse this line:\n %s\n", ptr);
+			goto nextline;
+		}
+		*arg++ = 0;
+		while (*arg == ' ' || *arg == '\t') {
+			arg++;
+		}
+		if (!strcasecmp("default", ptr)) {
+			defaultlabel = arg;
+		} else if (!strcasecmp("label", ptr)) {
+			entries[num_entries].label = arg;
+			if (defaultlabel && !strcmp(arg, defaultlabel)) {
+				*def_ent = num_entries;
+			}
+			num_entries++;
+		} else if (!strcasecmp("kernel", ptr) && num_entries) {
+			entries[num_entries - 1].kernel = arg;
+		} else if (!strcasecmp("initrd", ptr) && num_entries) {
+			entries[num_entries - 1].initrd = arg;
+		} else if (!strcasecmp("append", ptr) && num_entries) {
+			entries[num_entries - 1].append = arg;
+		} else {
+			printf("Command '%s' is not supported.\n", ptr);
+		}
+nextline:
+		ptr = nextptr;
+	}
+
+	return num_entries;
+}
+
+/**
+ * Try to load and parse a pxelinux-style configuration file.
+ * @param fn_ip        must contain server and client IP information
+ * @param mac          MAC address which should be used for probing
+ * @param retries      Amount of TFTP retries before giving up
+ * @param cfgbuf       Pointer to the buffer where config file should be loaded
+ * @param cfgsize      Size of the cfgbuf buffer
+ * @param entries      Pointer to array where the results should be put into
+ * @param max_entries  Number of available slots in the entries array
+ * @param def_ent      Used to return the index of the default entry
+ * @return             Number of valid entries
+ */
+int pxelinux_load_parse_cfg(filename_ip_t *fn_ip, uint8_t *mac,
+                            int retries, char *cfgbuf, int cfgsize,
+                            struct pl_cfg_entry *entries, int max_entries,
+                            int *def_ent)
+{
+	int rc;
+
+	rc = pxelinux_load_cfg(fn_ip, mac, retries, cfgbuf, cfgsize);
+	if (rc < 0)
+		return rc;
+
+	return pxelinux_parse_cfg(cfgbuf, rc, entries, max_entries, def_ent);
+}
diff --git a/lib/libnet/pxelinux.h b/lib/libnet/pxelinux.h
new file mode 100644
index 0000000..98b3925
--- /dev/null
+++ b/lib/libnet/pxelinux.h
@@ -0,0 +1,33 @@ 
+/*****************************************************************************
+ * Definitions for pxelinux-style config file support
+ *
+ * Copyright 2018 Red Hat, Inc.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the BSD License
+ * which accompanies this distribution, and is available at
+ * http://www.opensource.org/licenses/bsd-license.php
+ *
+ * Contributors:
+ *     Thomas Huth, Red Hat Inc. - initial implementation
+ *****************************************************************************/
+
+#ifndef LIBNET_PXELINUX_H
+#define LIBNET_PXELINUX_H
+
+/* This structure holds the data from one pxelinux.cfg file entry */
+struct pl_cfg_entry {
+    const char *label;
+    const char *kernel;
+    const char *initrd;
+    const char *append;
+};
+
+int pxelinux_parse_cfg(char *cfg, int cfgsize, struct pl_cfg_entry *entries,
+                       int max_entries, int *def_ent);
+int pxelinux_load_parse_cfg(filename_ip_t *fn_ip, uint8_t *mac,
+                            int retries, char *cfgbuf, int cfgsize,
+                            struct pl_cfg_entry *entries,
+                            int max_entries, int *def_ent);
+
+#endif