network boot: support loading complete ISOs via HTTP

Now I don't have to unpack (or loop mount) ISO to boot via HTTP.
Also I can boot directly from any ALT mirror, like this:

automatic=method:http,network:dhcp,server:mirror.yandex.ru,directory=/altlinux/images/p9/simply/aarch64/slinux-live-9.1.1-aarch64.iso

Closes: #40710

config-stage1.h

@@ -23,6 +23,7 @@
 #define IMAGE_LOCATION   "/image"
 #define STAGE2_LOCATION  "/root"
 #define LIVE_DEVICE	"/dev/loop0"
+#define LOMOUNT_DEVICE  "/dev/loop3"
 #define STAGE2FS	"squashfs"
 #define LIVEFS		"squashfs"
 #ifndef STAGE2_BINNAME

lomount.c

@@ -133,7 +133,7 @@ set_loop (const char *device, const char *file)
 }
 
 
-char * loopdev = "/dev/loop3"; /* Ugly. But do I care? */
+char * loopdev = LOMOUNT_DEVICE; /* Ugly. But do I care? */
 
 void del_loop(char *device)
 {

network.c

@@ -998,6 +998,7 @@ enum return_type http_prepare(void)
 		char *tmp;
 		int fd;
 		unsigned long size;
+		int is_iso = 0;
 
 		snprintf(location_full, sizeof(location_full),
 				 "Please enter the name or IP address of the HTTP server, "
@@ -1009,6 +1010,13 @@ enum return_type http_prepare(void)
 		}
 
 		strcpy(location_full, answers[1]);
+		log_message("HTTP: trying to retrieve %s", location_full);
+		fd = http_download_file(answers[0], location_full, &size);
+		if (fd >= 0) {
+			is_iso = 1;
+			goto download;
+		}
+
 		tmp = get_ramdisk_realname();
 		strcat(location_full, tmp);
 		free(tmp);
@@ -1026,6 +1034,7 @@ enum return_type http_prepare(void)
 			continue;
 		}
 
+	download:
 		if (!ramdisk_possible(size)) {
 			close(fd);
 			stg1_error_message("HTTP install needs more than %u Mbytes of memory (detected %u Mbytes).",
@@ -1035,7 +1044,7 @@ enum return_type http_prepare(void)
 
 		log_message("HTTP: size of download %lu bytes", size);
 
-		results = load_ramdisk_fd(fd, size);
+		results = load_ramdisk_or_iso(fd, size, is_iso);
 		close(fd);
 		if (results != RETURN_OK)
 			return RETURN_ERROR;

tools.c

@@ -45,6 +45,7 @@
 #include "automatic.h"
 #include <errno.h>
 #include <linux/loop.h>
+#include "lomount.h"
 #include "tools.h"
 #include "modules.h"
 #include "sha256.h"
@@ -297,6 +298,45 @@ static void save_stuff_for_rescue(void)
 	log_message("saved file %s for rescue (%d bytes)", file, i);
 }
 
+/**
+ * Loop mount ISO loaded to RAM, and open stage2
+ *
+ * @param ram_fd file descriptor of ISO image
+ * @return file descriptor of stage2 or -1 on error
+ */
+static int open_stage2_from_iso(int iso_fd)
+{
+	int stage2_fd = -1;
+	const char *stage2 = get_ramdisk_path(IMAGE_LOCATION); /* /image/live */
+	if (!stage2) {
+		log_message("%s: get_ramdisk_size: got NULL", __func__);
+		goto out;
+	}
+	if (do_losetup_fd(LOMOUNT_DEVICE, iso_fd, NULL) < 0) {
+		log_message("%s: could not setup loopback for iso_fd", __func__);
+		goto out_free;
+	}
+	if (my_mount(LOMOUNT_DEVICE, IMAGE_LOCATION, "iso9660", 0)) {
+		log_message("%s: failed to mount ISO loopback", __func__);
+		goto out_del_loop;
+	}
+	stage2_fd = open(stage2, O_RDONLY);
+	if (stage2_fd < 0) {
+		log_message("%s: failed to open %s", __func__, stage2);
+		goto out_umount;
+	}
+	free((char *)stage2);
+	return stage2_fd;
+
+out_umount:
+	umount(IMAGE_LOCATION);
+out_del_loop:
+	del_loop(LOMOUNT_DEVICE);
+out_free:
+	free((char *)stage2);
+out:
+	return -1;
+}
 
 /**
  * @brief copy exactly len bytes from buffer to file descriptor
@@ -382,7 +422,7 @@ out:
 	return -1;
 }
 
-enum return_type load_ramdisk_fd(int source_fd, unsigned long size)
+enum return_type load_ramdisk_or_iso(int source_fd, unsigned long size, int is_iso)
 {
 	int ram_fd;
 	char * wait_msg = "Loading program into memory...";
@@ -405,8 +445,26 @@ enum return_type load_ramdisk_fd(int source_fd, unsigned long size)
 	}
 	end_progression();
 
+	if (is_iso) {
+		int stage2_fd = open_stage2_from_iso(ram_fd);
+		if (stage2_fd < 0) {
+			close(ram_fd);
+			stg1_error_message("Could not open stage2 from ISO in RAM");
+			return RETURN_ERROR;
+		}
+		/* got a (mounted) loopback device backed by ram_fd,
+		 * ram_fd itself is not necessary any more */
+		close(ram_fd);
+		/* to setup loopback device from stage2_fd */
+		ram_fd = stage2_fd;
+	}
+
 	if (do_losetup_fd(LIVE_DEVICE, ram_fd, NULL) < 0) {
 		close(ram_fd);
+		if (is_iso) {
+			umount(IMAGE_LOCATION);
+			del_loop(LOMOUNT_DEVICE);
+		}
 		stg1_error_message("Could not setup loopback for 2nd stage");
 		return RETURN_ERROR;
 	}
@@ -416,6 +474,10 @@ enum return_type load_ramdisk_fd(int source_fd, unsigned long size)
 
 	if (my_mount(LIVE_DEVICE, STAGE2_LOCATION, STAGE2FS, 0)) {
 		stg1_error_message("Failed to mount stage2");
+		if (is_iso) {
+			umount(IMAGE_LOCATION);
+			del_loop(LOMOUNT_DEVICE);
+		}
 		return RETURN_ERROR;
 	}
 
@@ -427,12 +489,18 @@ enum return_type load_ramdisk_fd(int source_fd, unsigned long size)
 			log_message("rescue: failed to umount " STAGE2_LOCATION);
 			return RETURN_ERROR;
 		}
+		if (is_iso) {
+			/* XXX: should I do anything special here? */
+		}
 		return RETURN_OK; /* fucksike, I lost several hours wondering why the kernel won't see the rescue if it is alreay mounted */
 	}
 
 	return RETURN_OK;
 }
 
+enum return_type load_ramdisk_fd(int source_fd, unsigned long size) {
+	return load_ramdisk_or_iso(source_fd, size, 0);
+}
 
 int splash_verbose()
 {

tools.h

@@ -36,6 +36,7 @@ int ramdisk_possible(unsigned long ramdisk_size);
 char * get_ramdisk_realname(void);
 enum return_type load_ramdisk(char *, unsigned long size);
 enum return_type load_ramdisk_fd(int ramdisk_fd, unsigned long size);
+enum return_type load_ramdisk_or_iso(int ramdisk_fd, unsigned long size, int is_iso);
 void * memdup(void *src, size_t size);
 void add_to_env(char * name, char * value);
 void handle_env(char ** env);