From 35b93e247fbe3a76f656c4975f54a771f5d609fa Mon Sep 17 00:00:00 2001
From: Mark <alnyan@airmail.cc>
Date: Sat, 4 Jan 2020 20:11:40 +0200
Subject: [PATCH] Add support for GPT partitions

---
 sys/blk.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 79 insertions(+), 1 deletion(-)

diff --git a/sys/blk.c b/sys/blk.c
index 9b2ae52..8f1028c 100644
--- a/sys/blk.c
+++ b/sys/blk.c
@@ -29,6 +29,7 @@ ssize_t blk_write(struct blkdev *blk, const void *buf, size_t off, size_t lim) {
     }
 }
 
+const char GUID_EMPTY[16] = {0};
 
 // TODO: guess this would better be in blk_part.c or something like that
 struct mbr {
@@ -46,6 +47,32 @@ struct mbr {
     uint16_t sign;
 } __attribute__((packed));
 
+struct gpt_header {
+    char signature[8];
+    uint32_t revision;
+    uint32_t header_size;
+    uint32_t header_crc32;
+    uint32_t __res0;
+    uint64_t my_lba;
+    uint64_t alt_lba;
+    uint64_t first_lba;
+    uint64_t last_lba;
+    char disk_guid[16];
+    uint64_t partition_entry_lba;
+    uint32_t partition_count;
+    uint32_t partition_entry_size;
+    uint32_t partition_array_crc32;
+} __attribute__((packed));
+
+struct gpt_part_entry {
+    char type_guid[16];
+    char part_guid[16];
+    uint64_t start_lba;
+    uint64_t end_lba;
+    uint64_t attr;
+    char part_name[72];
+};
+
 struct blk_part {
     struct blkdev *device;
     uint64_t lba_start;
@@ -119,6 +146,56 @@ static int blk_enumerate_mbr(struct blkdev *dev, uint8_t *head) {
     return 0;
 }
 
+static int blk_enumerate_gpt(struct blkdev *dev, uint8_t *head) {
+    // LBA1 - GPT header
+    struct gpt_header *hdr = (struct gpt_header *) &head[512];
+    // Read a single block for partition table entries
+    char buf[512];
+
+    _assert(blk_read(dev, buf, hdr->partition_entry_lba * 512, 512) >= 0);
+
+    size_t offset = 0;
+    size_t part_n = 0;
+    for (size_t i = 0; i < hdr->partition_count; ++i) {
+        struct gpt_part_entry *ent = (struct gpt_part_entry *) &buf[offset];
+
+        if (strncmp(ent->type_guid, GUID_EMPTY, 16)) {
+            // Maybe some known filesystem here, ignore partition type guid
+
+            struct blk_part *part = (struct blk_part *) kmalloc(sizeof(struct blk_part));
+            part->device = dev;
+            part->lba_start = ent->start_lba;
+            part->lba_size = ent->end_lba - ent->start_lba;
+
+            void *buf = kmalloc(sizeof(struct blkdev) + sizeof(struct dev_entry));
+            struct dev_entry *ent = (struct dev_entry *) buf;
+            struct blkdev *blk = (struct blkdev *) ((uintptr_t) buf + sizeof(struct dev_entry));
+            _assert(ent);
+
+            blk->dev_data = part;
+            blk->read = blk_part_read;
+            blk->ent_parent = dev->ent;
+
+            ent->dev = blk;
+            ent->dev_class = DEV_CLASS_BLOCK;
+            ent->dev_subclass = DEV_BLOCK_PART;
+            // XXX: This is ugly
+            strcpy(ent->dev_name, dev->ent->dev_name);
+            char digit[2] = { '1' + part_n++, 0 };
+            strcat(ent->dev_name, digit);
+
+            dev_entry_add(ent);
+        }
+
+        offset += hdr->partition_entry_size;
+        if (offset >= 512) {
+            break;
+        }
+    }
+
+    return 0;
+}
+
 struct blkdev *blk_by_name(const char *name) {
     struct dev_entry *it = dev_iter();
 
@@ -133,13 +210,14 @@ struct blkdev *blk_by_name(const char *name) {
 
 int blk_enumerate_partitions(struct blkdev *dev) {
     kdebug("Enumerating partitions of %s\n", dev->ent->dev_name);
+    // TODO: handle stuff where block size is not 512
     uint8_t buf[1024];
 
     _assert(blk_read(dev, buf, 0, 1024) >= 0);
 
     if (!strncmp((const char *) (buf + 512), "EFI PART", 8)) {
         // Found GPT
-        panic("Found GPT: not supported\n");
+        return blk_enumerate_gpt(dev, buf);
     } else if (buf[510] == 0x55 && buf[511] == 0xAA) {
         // Found MBR
         return blk_enumerate_mbr(dev, buf);