:: commit 097175c6be7e33623478bc98b3088fa25e558b5f
fat: Improve detection code
diff --git a/common/fs/fat32.s2.c b/common/fs/fat32.s2.c
index 8ec7a1ad..3b74de92 100644
--- a/common/fs/fat32.s2.c
+++ b/common/fs/fat32.s2.c
@@ -9,42 +9,42 @@
#define FAT32_LFN_MAX_ENTRIES 20
#define FAT32_LFN_MAX_FILENAME_LENGTH (FAT32_LFN_MAX_ENTRIES * 13 + 1)
-#define FAT32_VALID_SIGNATURE_1 0x28
-#define FAT32_VALID_SIGNATURE_2 0x29
-#define FAT32_VALID_SYSTEM_IDENTIFIER "FAT32 "
-#define FAT16_VALID_SYSTEM_IDENTIFIER "FAT16 "
-#define FAT12_VALID_SYSTEM_IDENTIFIER "FAT12 "
#define FAT32_ATTRIBUTE_SUBDIRECTORY 0x10
#define FAT32_LFN_ATTRIBUTE 0x0F
struct fat32_bpb {
- uint8_t jump[3];
- char oem[8];
- uint16_t bytes_per_sector;
- uint8_t sectors_per_cluster;
- uint16_t reserved_sectors;
- uint8_t fats_count;
- uint16_t directory_entries_count;
- uint16_t sector_totals;
- uint8_t media_descriptor_type;
- uint16_t sectors_per_fat_16;
- uint16_t sectors_per_track;
- uint16_t heads_count;
- uint32_t hidden_sectors_count;
- uint32_t large_sectors_count;
- uint32_t sectors_per_fat_32;
- uint16_t flags;
- uint16_t fat_version_number;
- uint32_t root_directory_cluster;
- uint16_t fs_info_sector;
- uint16_t backup_boot_sector;
- uint8_t reserved[12];
- uint8_t drive_number;
- uint8_t nt_flags;
- uint8_t signature;
- uint32_t volume_serial_number;
- char label[11];
- char system_identifier[8];
+ union {
+ struct {
+ uint8_t jump[3];
+ char oem[8];
+ uint16_t bytes_per_sector;
+ uint8_t sectors_per_cluster;
+ uint16_t reserved_sectors;
+ uint8_t fats_count;
+ uint16_t root_entries_count;
+ uint16_t sectors_count_16;
+ uint8_t media_descriptor_type;
+ uint16_t sectors_per_fat_16;
+ uint16_t sectors_per_track;
+ uint16_t heads_count;
+ uint32_t hidden_sectors_count;
+ uint32_t sectors_count_32;
+ uint32_t sectors_per_fat_32;
+ uint16_t flags;
+ uint16_t fat_version_number;
+ uint32_t root_directory_cluster;
+ uint16_t fs_info_sector;
+ uint16_t backup_boot_sector;
+ uint8_t reserved[12];
+ uint8_t drive_number;
+ uint8_t nt_flags;
+ uint8_t signature;
+ uint32_t volume_serial_number;
+ char label[11];
+ char system_identifier[8];
+ } __attribute__((packed));
+ uint8_t padding[512];
+ };
} __attribute__((packed));
struct fat32_directory_entry {
@@ -74,26 +74,56 @@ static int fat32_init_context(struct fat32_context* context, struct volume *part
struct fat32_bpb bpb;
volume_read(context->part, &bpb, 0, sizeof(struct fat32_bpb));
- if (strncmp(bpb.system_identifier, FAT32_VALID_SYSTEM_IDENTIFIER, SIZEOF_ARRAY(bpb.system_identifier)) == 0) {
- if (bpb.signature == FAT32_VALID_SIGNATURE_1 || bpb.signature == FAT32_VALID_SIGNATURE_2) {
- context->type = 32;
- goto valid;
- }
+ // Generic check
+ if (*(uint16_t *)(((void *)&bpb) + 510) != 0xaa55) {
+ return 1;
}
- if (strncmp((((void *)&bpb) + 0x36), FAT16_VALID_SYSTEM_IDENTIFIER, SIZEOF_ARRAY(bpb.system_identifier)) == 0) {
- context->type = 16;
+ // Checks for FAT12/16
+ if (strncmp((((void *)&bpb) + 0x36), "FAT", 3) == 0) {
+ if (*(((uint8_t *)&bpb) + 0x26) != 0x29) {
+ for (size_t i = 0; i < 15; i++) {
+ if (*(((uint8_t *)&bpb) + 0x27 + i) != 0) {
+ return 1;
+ }
+ }
+ }
+
goto valid;
}
- if (strncmp((((void *)&bpb) + 0x36), FAT12_VALID_SYSTEM_IDENTIFIER, SIZEOF_ARRAY(bpb.system_identifier)) == 0) {
- context->type = 12;
+ // Checks for FAT32
+ if (strncmp((((void *)&bpb) + 0x52), "FAT", 3) == 0) {
+ if (*(((uint8_t *)&bpb) + 0x42) != 0x29) {
+ for (size_t i = 0; i < 15; i++) {
+ if (*(((uint8_t *)&bpb) + 0x43 + i) != 0) {
+ return 1;
+ }
+ }
+ }
+
goto valid;
}
return 1;
valid:
+ // The following mess to identify the FAT type is from the FAT spec
+ // at paragraph 3.5
+ size_t root_dir_sects = ((bpb.root_entries_count * 32) + (bpb.bytes_per_sector - 1)) / bpb.bytes_per_sector;
+
+ size_t data_sects = (bpb.sectors_count_16 ?: bpb.sectors_count_32) - (bpb.reserved_sectors + (bpb.fats_count * (bpb.sectors_per_fat_16 ?: bpb.sectors_per_fat_32)) + root_dir_sects);
+
+ size_t clusters_count = data_sects / bpb.sectors_per_cluster;
+
+ if (clusters_count < 4085) {
+ context->type = 12;
+ } else if (clusters_count < 65525) {
+ context->type = 16;
+ } else {
+ context->type = 32;
+ }
+
context->bytes_per_sector = bpb.bytes_per_sector;
context->sectors_per_cluster = bpb.sectors_per_cluster;
context->reserved_sectors = bpb.reserved_sectors;
@@ -102,7 +132,7 @@ valid:
context->sectors_per_fat = context->type == 32 ? bpb.sectors_per_fat_32 : bpb.sectors_per_fat_16;
context->root_directory_cluster = bpb.root_directory_cluster;
context->fat_start_lba = bpb.reserved_sectors;
- context->root_entries = bpb.directory_entries_count;
+ context->root_entries = bpb.root_entries_count;
context->root_start = context->reserved_sectors + context->number_of_fats * context->sectors_per_fat;
context->root_size = DIV_ROUNDUP(context->root_entries * sizeof(struct fat32_directory_entry), context->bytes_per_sector);
switch (context->type) {
diff --git a/common/lib/part.s2.c b/common/lib/part.s2.c
index ed3e51bb..43107dbc 100644
--- a/common/lib/part.s2.c
+++ b/common/lib/part.s2.c
@@ -295,6 +295,9 @@ static int mbr_get_part(struct volume *ret, struct volume *volume, int partition
volume_read(volume, hintc, 54, 3);
if (memcmp(hintc, "FAT", 3) == 0)
return INVALID_TABLE;
+ volume_read(volume, hintc, 82, 3);
+ if (memcmp(hintc, "FAT", 3) == 0)
+ return false;
volume_read(volume, &hint, 1080, sizeof(uint16_t));
if (hint == 0xef53)
return INVALID_TABLE;
diff --git a/limine-install/limine-install.c b/limine-install/limine-install.c
index cdfd9c79..b24fbff3 100644
--- a/limine-install/limine-install.c
+++ b/limine-install/limine-install.c
@@ -482,6 +482,15 @@ int main(int argc, char *argv[]) {
device_write(hintc, 54, 5);
}
}
+ device_read(hintc, 82, 3);
+ if (memcmp(hintc, "FAT", 3) == 0) {
+ if (!force_mbr) {
+ mbr = 0;
+ } else {
+ memset(hintc, 0, 5);
+ device_write(hintc, 82, 5);
+ }
+ }
device_read(&hint16, 1080, sizeof(uint16_t));
hint16 = ENDSWAP(hint16);
if (hint16 == 0xef53) {
