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Bootloader: Add support for ext2 blocks up to 4 KiB 

This should work with blocks bigger than that, but my linux system
only supports up to 4 KiB, so I cannot test this.

This allows getting rid of forced block size in mkfs and let the
program select appropriately sized blocks.
This commit is contained in:
Bananymous 2024-01-03 18:26:03 +02:00
parent 7356a83a44
commit ccaa159a73
2 changed files with 109 additions and 91 deletions
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198
bootloader/bios/ext2.S
View File

@ -2,9 +2,7 @@
.set SECTOR_SHIFT, 9 .set SECTOR_SHIFT, 9
.set SECTOR_SIZE, 1 << SECTOR_SHIFT .set SECTOR_SIZE, 1 << SECTOR_SHIFT
# FIXME: don't assume 1024 byte blocks .set EXT2_MAX_BLOCK_SIZE, 4096
.set EXT2_BLOCK_SHIFT, 10
.set EXT2_BLOCK_SIZE, 1 << EXT2_BLOCK_SHIFT
.set EXT2_SUPERBLOCK_SIZE, 264 .set EXT2_SUPERBLOCK_SIZE, 264
.set EXT2_BGD_SHIFT, 5 .set EXT2_BGD_SHIFT, 5
.set EXT2_BGD_SIZE, 1 << EXT2_BGD_SHIFT .set EXT2_BGD_SIZE, 1 << EXT2_BGD_SHIFT
@ -18,6 +16,7 @@
.set EXT2_S_IFREG, 0x8000 .set EXT2_S_IFREG, 0x8000
# superblock offsets # superblock offsets
.set s_first_data_block, 20
.set s_log_block_size, 24 .set s_log_block_size, 24
.set s_inodes_per_group, 40 .set s_inodes_per_group, 40
.set s_magic, 56 .set s_magic, 56
@ -66,9 +65,7 @@ has_ext2_filesystem:
# from byte offset 1024 # from byte offset 1024
addl $(1024 / SECTOR_SIZE), %eax addl $(1024 / SECTOR_SIZE), %eax
jnc .has_ext2_filesystem_no_overflow adcw $0, %bx
incw %bx
.has_ext2_filesystem_no_overflow:
# into sector buffer # into sector buffer
movw $ext2_block_buffer, %di movw $ext2_block_buffer, %di
@ -90,11 +87,16 @@ has_ext2_filesystem:
movl (ext2_superblock_buffer + s_log_block_size), %ecx movl (ext2_superblock_buffer + s_log_block_size), %ecx
testl $0xFFFFFF00, %ecx testl $0xFFFFFF00, %ecx
jnz .has_ext2_filesystem_unsupported_block_size jnz .has_ext2_filesystem_unsupported_block_size
# verify 1024 << s_log_block_size == EXT2_BLOCK_SIZE # verify 1024 << s_log_block_size <= EXT2_MAX_BLOCK_SIZE
movl $1024, %eax movl $1024, %eax
shll %cl, %eax shll %cl, %eax
cmpl $EXT2_BLOCK_SIZE, %eax cmpl $EXT2_MAX_BLOCK_SIZE, %eax
jne .has_ext2_filesystem_unsupported_block_size ja .has_ext2_filesystem_unsupported_block_size
# fill block size and shift
movl %eax, (ext2_block_size)
addl $10, %ecx
movl %ecx, (ext2_block_shift)
# fill inode size # fill inode size
movl $128, %eax movl $128, %eax
@ -130,38 +132,23 @@ has_ext2_filesystem:
# reads block in to ext2_block_buffer # reads block in to ext2_block_buffer
# eax: block number # eax: block number
ext2_read_block: ext2_read_block:
pushl %eax pushal
pushl %ebx
pushw %cx
pushl %edx
pushw %di
# NOTE: this assumes 1024 block size # ecx := sectors_per_block := block_size / sector_size
# eax := (block * block_size) / sector_size := (eax << EXT2_BLOCK_SHIFT) >> SECTOR_SHIFT movl (ext2_block_size), %ecx
xorl %edx, %edx shrl $SECTOR_SHIFT, %ecx
shll $EXT2_BLOCK_SHIFT, %eax
shrl $SECTOR_SHIFT, %eax
# ebx:eax := eax + (ext2_partition_first_sector) # ebx:eax := block * sectors_per_block + (ext2_partition_first_sector)
movl (ext2_partition_first_sector + 4), %ebx xorl %ebx, %ebx
mull %ecx
addl (ext2_partition_first_sector + 0), %eax addl (ext2_partition_first_sector + 0), %eax
jnc .ext2_read_block_no_carry adcl (ext2_partition_first_sector + 4), %ebx
incl %ebx
.ext2_read_block_no_carry:
# sectors per block
movw $(EXT2_BLOCK_SIZE / SECTOR_SIZE), %cx
movw $ext2_block_buffer, %di movw $ext2_block_buffer, %di
movb (ext2_drive_number), %dl movb (ext2_drive_number), %dl
call read_from_disk call read_from_disk
popw %di popal
popl %edx
popw %cx
popl %ebx
popl %eax
ret ret
@ -170,15 +157,23 @@ ext2_read_block:
ext2_read_block_group_descriptor: ext2_read_block_group_descriptor:
pushal pushal
# eax := bgd_byte_offset := 2048 + EXT2_BGD_SIZE * eax := (eax << EXT2_BGD_SHIFT) + 2048 # ebx := bgd_block_byte_offset := (s_first_data_block + 1) * block_size
shll $EXT2_BGD_SHIFT, %eax # := (s_first_data_block + 1) << ext2_block_shift
addl $2048, %eax movl (ext2_superblock_buffer + s_first_data_block), %ebx
incl %ebx
movb (ext2_block_shift), %cl
shll %cl, %ebx
# eax: bgd_block := bgd_byte_offset / EXT2_BLOCK_SIZE # eax := bgd_byte_offset := bgd_block_byte_offset + EXT2_BGD_SIZE * block_group;
# ebx: bgd_offset := bgd_byte_offset % EXT2_BLOCK_SIZE # := bgd_block_byte_offset + (block_group << EXT2_BGD_SHIFT)
movb $EXT2_BGD_SHIFT, %cl
shll %cl, %eax
addl %ebx, %eax
# eax: bgd_block := bgd_byte_offset / block_size
# ebx: bgd_offset := bgd_byte_offset % block_size
xorl %edx, %edx xorl %edx, %edx
movl $EXT2_BLOCK_SIZE, %ebx divl (ext2_block_size)
divl %ebx
movl %edx, %ebx movl %edx, %ebx
call ext2_read_block call ext2_read_block
@ -204,23 +199,19 @@ ext2_read_inode:
# ebx := inode_index = (ino - 1) % s_inodes_per_group # ebx := inode_index = (ino - 1) % s_inodes_per_group
xorl %edx, %edx xorl %edx, %edx
decl %eax decl %eax
movl (ext2_superblock_buffer + s_inodes_per_group), %ebx divl (ext2_superblock_buffer + s_inodes_per_group)
divl %ebx
movl %edx, %ebx movl %edx, %ebx
call ext2_read_block_group_descriptor call ext2_read_block_group_descriptor
# eax := inode_table_block := (inode_index * inode_size) / EXT2_BLOCK_SIZE # eax := inode_table_block := (inode_index * inode_size) / block_size
# ebx := inode_table_offset := (inode_index * inode_size) % EXT2_BLOCK_SIZE # ebx := inode_table_offset := (inode_index * inode_size) % block_size
xorl %edx, %edx
movl %ebx, %eax movl %ebx, %eax
movl (ext2_inode_size), %ebx mull (ext2_inode_size)
mull %ebx divl (ext2_block_size)
movl $EXT2_BLOCK_SIZE, %ebx
divl %ebx
movl %edx, %ebx movl %edx, %ebx
# eax := file system block := eax + bg_inode_table # eax := filesystem_block := eax + bg_inode_table
addl (ext2_block_group_descriptor_buffer + bg_inode_table), %eax addl (ext2_block_group_descriptor_buffer + bg_inode_table), %eax
movb (ext2_drive_number), %dl movb (ext2_drive_number), %dl
@ -255,14 +246,17 @@ ext2_data_block_index:
pushl %esi pushl %esi
pushl %edi pushl %edi
# calculate max data blocks # ebx := max_data_blocks := (file_size + block_size - 1) / block_size
movl (ext2_inode_buffer + i_size), %ecx # := (i_size + ext2_block_size - 1) >> ext2_block_shift
addl (ext2_inode_size), %ecx # cl := ext2_block_shift
decl %ecx movl (ext2_inode_buffer + i_size), %ebx
shll $EXT2_BLOCK_SHIFT, %ecx addl (ext2_block_size), %ebx
decl %ebx
movb (ext2_block_shift), %cl
shrl %cl, %ebx
# verify data block is within bounds # verify data block is within bounds
cmpl %ecx, %eax cmpl %ebx, %eax
jae .ext2_data_block_index_out_of_bounds jae .ext2_data_block_index_out_of_bounds
# check if this is direct block access # check if this is direct block access
@ -270,18 +264,26 @@ ext2_data_block_index:
jb .ext2_data_block_index_direct jb .ext2_data_block_index_direct
subl $12, %eax subl $12, %eax
# cl := indices_per_block_shift := ext2_block_shift - 2
# ebx := comp
subb $2, %cl
movl $1, %ebx
shll %cl, %ebx
# check if this is singly indirect block access # check if this is singly indirect block access
cmpl $(EXT2_BLOCK_SIZE / 4), %eax cmpl %ebx, %eax
jb .ext2_data_block_index_singly_indirect jb .ext2_data_block_index_singly_indirect
subl $(EXT2_BLOCK_SIZE / 4), %eax subl %ebx, %eax
shll %cl, %ebx
# check if this is doubly indirect block access # check if this is doubly indirect block access
cmpl $((EXT2_BLOCK_SIZE / 4) * (EXT2_BLOCK_SIZE / 4)), %eax cmpl %ebx, %eax
jb .ext2_data_block_index_doubly_indirect jb .ext2_data_block_index_doubly_indirect
subl $((EXT2_BLOCK_SIZE / 4) * (EXT2_BLOCK_SIZE / 4)), %eax subl %ebx, %eax
shll %cl, %ebx
# check if this is triply indirect block access # check if this is triply indirect block access
cmpl $((EXT2_BLOCK_SIZE / 4) * (EXT2_BLOCK_SIZE / 4) * (EXT2_BLOCK_SIZE / 4)), %eax cmpl %ebx, %eax
jb .ext2_data_block_index_triply_indirect jb .ext2_data_block_index_triply_indirect
# otherwise this is invalid access # otherwise this is invalid access
@ -314,9 +316,12 @@ ext2_data_block_index:
# ebx := index # ebx := index
# cx := depth # cx := depth
.ext2_data_block_index_indirect: .ext2_data_block_index_indirect:
# calculate cache index ((index & 0xFF) | depth) # edx := cache index := (index & ~(block_size / 4 - 1)) | depth
movl %ebx, %edx # := (index & -(block_size >> 2)) | depth
andl $(~(EXT2_BLOCK_SIZE / 4 - 1)), %edx movl (ext2_block_size), %edx
shrl $2, %edx
negl %edx
andl %ebx, %edx
orw %cx, %dx orw %cx, %dx
# check whether this block is already cached # check whether this block is already cached
@ -343,20 +348,21 @@ ext2_data_block_index:
jbe .ext2_data_block_index_no_shift jbe .ext2_data_block_index_no_shift
# cl := shift # cl := shift
movb $(EXT2_BLOCK_SHIFT - 2), %al movb (ext2_block_shift), %al
subb $2, %al
decb %cl decb %cl
mulb %cl mulb %cl
movb %al, %cl movb %al, %cl
# ebx := ebx >> cl # ebx := ebx >> shift
shrl %cl, %ebx shrl %cl, %ebx
.ext2_data_block_index_no_shift: .ext2_data_block_index_no_shift:
# edx := index of next block # edx := index of next block (ebx & (block_size / 4 - 1))
movl %ebx, %eax movl (ext2_block_size), %edx
xorl %edx, %edx shrl $2, %edx
movl $(EXT2_BLOCK_SIZE / 4), %ebx decl %edx
divl %ebx andl %ebx, %edx
# eax := next block # eax := next block
movl $ext2_block_buffer, %esi movl $ext2_block_buffer, %esi
@ -371,7 +377,7 @@ ext2_data_block_index:
# cache last read block # cache last read block
movw $ext2_block_buffer, %si movw $ext2_block_buffer, %si
movw $ext2_inode_indirect_buffer, %di movw $ext2_inode_indirect_buffer, %di
movw $EXT2_BLOCK_SIZE, %cx movw (ext2_block_size), %cx
rep movsb rep movsb
jmp .ext2_data_block_index_done jmp .ext2_data_block_index_done
@ -390,7 +396,10 @@ ext2_data_block_index:
.ext2_data_block_index_indirect_cached: .ext2_data_block_index_indirect_cached:
movl $ext2_inode_indirect_buffer, %esi movl $ext2_inode_indirect_buffer, %esi
andl $(EXT2_BLOCK_SIZE / 4 - 1), %ebx movl (ext2_block_size), %edx
shrl $2, %edx
decl %edx
andl %edx, %ebx
movl (%esi, %ebx, 4), %eax movl (%esi, %ebx, 4), %eax
.ext2_data_block_index_done: .ext2_data_block_index_done:
@ -410,6 +419,7 @@ ext2_data_block_index:
.global ext2_inode_read_bytes .global ext2_inode_read_bytes
ext2_inode_read_bytes: ext2_inode_read_bytes:
pushal pushal
pushl %ebp pushl %ebp
movl %esp, %ebp movl %esp, %ebp
subl $8, %esp subl $8, %esp
@ -418,11 +428,11 @@ ext2_inode_read_bytes:
movl %eax, 0(%esp) movl %eax, 0(%esp)
movl %ecx, 4(%esp) movl %ecx, 4(%esp)
# check if eax % EXT2_BLOCK_SIZE != 0, # eax := first_byte / block_size
# then we need to read a partial block starting from an offset # edx := first_byte % block_size
# when edx == 0, no partial read needed
xorl %edx, %edx xorl %edx, %edx
movl $EXT2_BLOCK_SIZE, %ebx divl (ext2_block_size)
divl %ebx
testl %edx, %edx testl %edx, %edx
jz .ext2_inode_read_bytes_no_partial_start jz .ext2_inode_read_bytes_no_partial_start
@ -431,7 +441,7 @@ ext2_inode_read_bytes:
call ext2_read_block call ext2_read_block
# ecx := byte count (min(block_size - edx, remaining_bytes)) # ecx := byte count (min(block_size - edx, remaining_bytes))
movl $EXT2_BLOCK_SIZE, %ecx movl (ext2_block_size), %ecx
subl %edx, %ecx subl %edx, %ecx
cmpl %ecx, 4(%esp) cmpl %ecx, 4(%esp)
cmovbl 4(%esp), %ecx cmovbl 4(%esp), %ecx
@ -445,7 +455,7 @@ ext2_inode_read_bytes:
addl %edx, %esi addl %edx, %esi
# very dumb memcpy with 32 bit addresses # very dumb memcpy with 32 bit addresses
movl $0, %ebx xorl %ebx, %ebx
.ext2_inode_read_bytes_memcpy_partial: .ext2_inode_read_bytes_memcpy_partial:
movb (%esi, %ebx), %al movb (%esi, %ebx), %al
movb %al, (%edi, %ebx) movb %al, (%edi, %ebx)
@ -461,14 +471,15 @@ ext2_inode_read_bytes:
.ext2_inode_read_bytes_no_partial_start: .ext2_inode_read_bytes_no_partial_start:
# eax := data block index (byte_start / block_size) # eax := data block index (byte_start / block_size)
movl 0(%esp), %eax movl 0(%esp), %eax
shrl $(EXT2_BLOCK_SHIFT), %eax movb (ext2_block_shift), %cl
shrl %cl, %eax
# get data block index and read block # get data block index and read block
call ext2_data_block_index call ext2_data_block_index
call ext2_read_block call ext2_read_block
# calculate bytes to copy (min(block_size, remaining_bytes)) # calculate bytes to copy (min(block_size, remaining_bytes))
movl $EXT2_BLOCK_SIZE, %ecx movl (ext2_block_size), %ecx
cmpl %ecx, 4(%esp) cmpl %ecx, 4(%esp)
cmovbl 4(%esp), %ecx cmovbl 4(%esp), %ecx
@ -524,11 +535,12 @@ ext2_directory_find_inode:
cmpw $0xFF, %cx cmpw $0xFF, %cx
ja .ext2_directory_find_inode_not_found ja .ext2_directory_find_inode_not_found
# ebx := max data blocks: ceil(i_size / EXT2_BLOCK_SIZE) # ebx := max data blocks: ceil(i_size / block_size)
movl (ext2_inode_buffer + i_size), %ebx movl (ext2_inode_buffer + i_size), %ebx
addl $EXT2_BLOCK_SHIFT, %ebx addl (ext2_block_size), %ebx
decl %ebx decl %ebx
shrl $EXT2_BLOCK_SHIFT, %ebx movb (ext2_block_shift), %cl
shrl %cl, %ebx
jz .ext2_directory_find_inode_not_found jz .ext2_directory_find_inode_not_found
# 4(%esp) := current block # 4(%esp) := current block
@ -575,7 +587,9 @@ ext2_directory_find_inode:
# go to next entry if this block contains one # go to next entry if this block contains one
addw 4(%si), %si addw 4(%si), %si
cmpw $(ext2_block_buffer + EXT2_BLOCK_SIZE), %si movw $ext2_block_buffer, %di
addw (ext2_block_size), %di
cmpw %di, %si
jb .ext2_directory_find_inode_loop_entries jb .ext2_directory_find_inode_loop_entries
.ext2_directory_find_inode_next_block: .ext2_directory_find_inode_next_block:
@ -584,7 +598,7 @@ ext2_directory_find_inode:
jb .ext2_directory_find_inode_block_read_loop jb .ext2_directory_find_inode_block_read_loop
.ext2_directory_find_inode_not_found: .ext2_directory_find_inode_not_found:
movb $0, %al xorb %al, %al
jmp .ext2_directory_find_inode_done jmp .ext2_directory_find_inode_done
.ext2_directory_find_inode_found: .ext2_directory_find_inode_found:
@ -696,7 +710,7 @@ root_partition_does_not_fit_ext2_filesystem_msg:
root_partition_has_invalid_ext2_magic_msg: root_partition_has_invalid_ext2_magic_msg:
.asciz "Root partition doesn't contain ext2 magic number" .asciz "Root partition doesn't contain ext2 magic number"
root_partition_has_unsupported_ext2_block_size_msg: root_partition_has_unsupported_ext2_block_size_msg:
.asciz "Root partition has unsupported ext2 block size (only 1024 supported)" .asciz "Root partition has unsupported ext2 block size (1 KiB, 2 KiB and 4 KiB are supported)"
ext2_part_not_dir_msg: ext2_part_not_dir_msg:
.asciz "inode in root path is not directory" .asciz "inode in root path is not directory"
@ -717,12 +731,12 @@ ext2_looking_for_msg:
.section .bss .section .bss
.align EXT2_BLOCK_SIZE .align SECTOR_SIZE
ext2_block_buffer: ext2_block_buffer:
.skip EXT2_BLOCK_SIZE .skip EXT2_MAX_BLOCK_SIZE
ext2_inode_indirect_buffer: ext2_inode_indirect_buffer:
.skip EXT2_BLOCK_SIZE .skip EXT2_MAX_BLOCK_SIZE
ext2_inode_indirect_number: ext2_inode_indirect_number:
.skip 4 .skip 4
@ -736,6 +750,10 @@ ext2_drive_number:
# NOTE: fits in 2 bytes # NOTE: fits in 2 bytes
ext2_inode_size: ext2_inode_size:
.skip 4 .skip 4
ext2_block_size:
.skip 4
ext2_block_shift:
.skip 4
ext2_superblock_buffer: ext2_superblock_buffer:
.skip EXT2_SUPERBLOCK_SIZE .skip EXT2_SUPERBLOCK_SIZE

2
script/image-create.sh
View File

@ -87,7 +87,7 @@ sudo partprobe $LOOP_DEV
PARTITION1=${LOOP_DEV}p1 PARTITION1=${LOOP_DEV}p1
PARTITION2=${LOOP_DEV}p2 PARTITION2=${LOOP_DEV}p2
sudo mkfs.ext2 -q -b 1024 $PARTITION2 sudo mkfs.ext2 -q $PARTITION2
sudo mkdir -p $MOUNT_DIR || { echo "Failed to create banan mount dir."; exit 1; } sudo mkdir -p $MOUNT_DIR || { echo "Failed to create banan mount dir."; exit 1; }