1 files changed, 135 insertions, 0 deletions
diff --git a/kernel/initrd.c b/kernel/initrd.c
new file mode 100644
index 0000000..c05e77d
--- /dev/null
+++ b/kernel/initrd.c
@@ -0,0 +1,135 @@
+#include <fbos/init.h>
+#include <fbos/sched.h>
+#include <fbos/printk.h>
+#include <fbos/string.h>
+
+#define BUFFER_SIZE 16
+
+#define CPIO_HEADER_FILESIZE 54
+#define CPIO_HEADER_NAMESIZE 94
+#define CPIO_HEADER_SIZE 110
+
+// TODO: move to assembly
+__kernel void *memcpy(void *dest, const void *src, size_t count)
+{
+	char *destc = dest;
+	const char *srcc = src;
+
+	for (uint64_t i = 0; i < count; i++) {
+		*destc++ = *srcc++;
+	}
+	return dest;
+}
+
+// TODO: this is required by GCC which must be doing some optimization
+// underneath. For now let's keep it simple (and wrong) by just calling memcpy.
+__kernel void *memmove(void *dest, const void *src, size_t count)
+{
+	return memcpy(dest, src, count);
+}
+
+__kernel uint64_t strtoul16(const char *str, size_t count)
+{
+	char c;
+	uint64_t ret = 0;
+	uint64_t aux = 0;
+
+	for (uint64_t i = 1; count > 0; i *= 16, count--) {
+		c = str[count - 1];
+		if (c >= 'A' && c <= 'F') {
+			aux = 10 + (uint64_t)(c - 'A');
+		} else if (c >= 'a' && c <= 'f') {
+			aux = 10 + (uint64_t)(c - 'a');
+		} else if (c < '0' || c > '9') {
+			die("Bad number\n");
+		} else {
+			aux = (uint64_t)c - '0';
+		}
+
+		ret += aux * i;
+	}
+	return ret;
+}
+
+__kernel int get_task_id_from_name(const char *const name)
+{
+	if (strcmp(name, "usr/bin/foo") == 0) {
+		return TASK_FOO;
+	} else if (strcmp(name, "usr/bin/bar") == 0) {
+		return TASK_BAR;
+	} else if (strcmp(name, "usr/bin/foobar") == 0) {
+		return TASK_FOOBAR;
+	}
+	return TASK_UNKNOWN;
+}
+
+__kernel void extract_elf(int task_id, const char *const addr, size_t size)
+{
+	__unused(task_id);
+	__unused(addr);
+	__unused(size);
+
+	// TODO
+}
+
+__kernel void extract_initrd(const char *const initrd_addr, uint64_t size)
+{
+	char buffer[BUFFER_SIZE];
+	uint64_t name_size, file_size, padding, base = 0;
+	int task_id;
+
+	// The `base` is the index from `initrd_addr` which points to the first byte
+	// of the header of the currently evaluated file inside of the CPIO archive.
+	while (base < size) {
+		// Only the "newc" format is supported, without checksums nor fancy
+		// stuff.
+		if (memcmp(&initrd_addr[base], "070701", 6) != 0) {
+			if (memcmp(&initrd_addr[base], "070702", 6) == 0 ||
+				memcmp(&initrd_addr[base], "070707", 6) == 0) {
+				die("Incorrect cpio format: stick to 'newc'");
+			} else {
+				die("No cpio magic number");
+			}
+		}
+
+		// We identify the task being extracted by looking at the file's path,
+		// so let's first get the size of it.
+		memcpy(buffer, &initrd_addr[base + CPIO_HEADER_NAMESIZE], 8);
+		buffer[8] = '\0';
+		name_size = strtoul16(buffer, 8);
+		if (name_size >= BUFFER_SIZE) {
+			die("Path too large for initrd executable");
+		}
+
+		// Right after the header (hence current header + its size) there is the
+		// actual file's path, which is exactly `name_size` long. Fetch it now
+		// to identify the task at hand.
+		memcpy(buffer, &initrd_addr[base + CPIO_HEADER_SIZE], name_size);
+		buffer[name_size] = '\0';
+		task_id = get_task_id_from_name(buffer);
+
+		// Note that this is not necessarily a bad CPIO archive, it might just
+		// be the end "TRAILER!!!" delimiter. Either way, just quit at this
+		// point.
+		if (task_id == TASK_UNKNOWN) {
+			break;
+		}
+
+		// Fetch the size of the executable, which is needed for `extract_elf`,
+		// as well as for advancing the `base` to the next file.
+		memcpy(buffer, &initrd_addr[base + CPIO_HEADER_FILESIZE], 8);
+		buffer[8] = '\0';
+		file_size = strtoul16(buffer, 8);
+
+		// Files are aligned in 4-byte boundaries after the header. That's why
+		// there might be some padding in between the header and the file.
+		padding = 4 - ((CPIO_HEADER_SIZE + name_size) & 3);
+
+		// And extract everything from the ELF file for the given task.
+		extract_elf(task_id, &initrd_addr[base + name_size + CPIO_HEADER_SIZE + padding],
+					file_size);
+
+		// Advance the base to the next file.
+		base += CPIO_HEADER_SIZE + name_size + padding + file_size;
+	}
+}