feat(fs): add USTAR ramdisk parser

src/initrd.c

@@ -0,0 +1,108 @@
+#include "initrd.h"
+#include "string.h"
+#include "console.h"
+
+typedef struct UstarHeader {
+    char name[100];
+    char mode[8];
+    char uid[8];
+    char gid[8];
+    char size[12];
+    char mtime[12];
+    char checksum[8];
+    char typeflag;
+    char linkname[100];
+    char magic[6];
+    char version[2];
+    char uname[32];
+    char gname[32];
+    char devmajor[8];
+    char devminor[8];
+    char prefix[155];
+    char padding[12];
+} __attribute__((packed)) UstarHeader;
+
+static const uint8* archiveBase;
+static const uint8* archiveLimit;
+
+static uint64 parseOctal(const char* field, uint32 length)
+{
+    uint64 value = 0;
+    uint32 i = 0;
+    while (i < length && (field[i] == ' ' || field[i] == 0))
+        i++;
+    while (i < length && field[i] >= '0' && field[i] <= '7') {
+        value = (value << 3) | (uint64)(field[i] - '0');
+        i++;
+    }
+    return value;
+}
+
+static bool validMagic(const UstarHeader* header)
+{
+    return header->magic[0] == 'u' && header->magic[1] == 's' &&
+           header->magic[2] == 't' && header->magic[3] == 'a' &&
+           header->magic[4] == 'r';
+}
+
+void initrdInit(uint64 start, uint64 end)
+{
+    archiveBase = (const uint8*)start;
+    archiveLimit = (const uint8*)end;
+
+    if (end <= start || (end - start) < 512) {
+        archiveBase = nullptr;
+        archiveLimit = nullptr;
+        kprintf("[ustar] module too small or missing\n");
+        return;
+    }
+    kprintf("[ustar] archive at %p-%p (%lu KiB)\n",
+            (void*)start, (void*)end, (end - start) / 1024);
+}
+
+static bool walk(uint32 wanted, UstarEntry* out, uint32* total)
+{
+    if (!archiveBase)
+        return false;
+
+    const uint8* cursor = archiveBase;
+    uint32 index = 0;
+
+    while (cursor + 512 <= archiveLimit) {
+        const UstarHeader* header = (const UstarHeader*)cursor;
+        if (header->name[0] == 0)
+            break;
+        if (!validMagic(header))
+            break;
+
+        uint64 size = parseOctal(header->size, sizeof(header->size));
+
+        if (out && index == wanted) {
+            out->name = header->name;
+            out->data = cursor + 512;
+            out->size = size;
+            out->isDir = header->typeflag == '5';
+            return true;
+        }
+
+        uint64 advance = 512 + ((size + 511) & ~(uint64)511);
+        cursor += advance;
+        index++;
+    }
+
+    if (total)
+        *total = index;
+    return false;
+}
+
+uint32 initrdCount(void)
+{
+    uint32 total = 0;
+    walk((uint32)-1, nullptr, &total);
+    return total;
+}
+
+bool initrdAt(uint32 index, UstarEntry* out)
+{
+    return walk(index, out, nullptr);
+}