1. I am not familiar with freebsd, and don know if freebsd get the same issue,
But I do found the freebsd has some code snippets related to unwritten extent,
see: https://github.com/freebsd/freebsd-src/blob/b3f46656393f5c8a6e8305afeb5e8c3638025c26/sys/fs/ext2fs/ext2_extents.h#L37
https://github.com/freebsd/freebsd-src/blob/b3f46656393f5c8a6e8305afeb5e8c3638025c26/sys/fs/ext2fs/ext2_extents.c#L1347
Is Ext4 is freebsd's default/major file system ?

2. I did't look at linux kernel(ext4) berfor send this patch, I cant
found any offcial document, so I refer to linux source as a standand
when send this patch

3. Yes, unwritten extents are wild used, usally when a file cotains many
zeros, or mark file holes(fallocate, qemu-img...)
You can generate a file contains a lot of unwritten extents by qemu, for
example:
qemu-img convert -f raw -O qcow2 win10.img win10.qcow2
# win10.img's size: 10G
But for files do not have any continuous zeros, like compressed files,
then there will be no any unwritten extents
unwritten extents are usally seen in very large files

4. You can fix the typos, My English is not so good

On Oct 27 2021, at 10:56 pm, Pedro Falcato <pedro.falcato@gmail.com> wrote:

> Hi,
> 
> The patch looks OK despite the typos and lack of proper formatting on
> the commit message.
> 
> But honestly, I don't know if this patch is even mergeable considering
> you looked at the Linux kernel's source code for this. The patch was
> already trivial enough
> if you looked at the documentation and the FreeBSD driver (as I had
> done in the past but never got to fixing this considering I don't even
> know if unwritten extents can appear in the wild).
> 
> I *cannot* stress this enough: Ext4Pkg is a clean room implementation
> of ext4 licensed under the BSD-2-Clause-Patent license (which is NOT
> compatible with GPLv2) and cannot have random Linux kernel
> bits, or any other incompatibly-licensed project's bits for that matter.
> 
> Best regards,
> Pedro
> 
> 
>> On Wed, Oct 27, 2021 at 2:37 PM qi zhou <atmgnd@outlook.com> wrote:
>> 
>>> From: "Qi Zhou" <atmgnd@outlook.com>
>>> Subject: [PATCH] unwritten extent suuport
>>> 
>>> the real lenght of uninitialized/unwritten extent should be (ee_len
>>> - (1UL << 15)), and
>>> all related block should been read as zeros. see:
>>> https://github.com/torvalds/linux/blob/d25f27432f80a800a3592db128254c8140bd71bf/fs/ext4/ext4_extents.h#L156
>>> 
>>> Signed-off-by: Qi Zhou <atmgnd@outlook.com>
>>> ---
>>>  Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h | 5 +++++
>>>  Features/Ext4Pkg/Ext4Dxe/Extents.c  | 4 ++--
>>>  Features/Ext4Pkg/Ext4Dxe/Inode.c    | 5 +++++
>>>  3 files changed, 12 insertions(+), 2 deletions(-)
>>> 
>>> diff --git a/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h b/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
>>> index 070eb5a..7ca8eee 100644
>>> --- a/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
>>> +++ b/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
>>> @@ -402,6 +402,11 @@ typedef struct {
>>> 
>>>  #define EXT4_MIN_DIR_ENTRY_LEN  8
>>> 
>>> +#define EXTENT_INIT_MAX_LEN (1UL << 15)
>>> +
>>> +#define EXTENT_REAL_LEN(x) ((UINT16)(x <= EXTENT_INIT_MAX_LEN ? x :
>>> (x - EXTENT_INIT_MAX_LEN)))
>>> +#define EXTENT_IS_UNWRITTEN(x) (x > EXTENT_INIT_MAX_LEN)
>>> +
>>>  // This on-disk structure is present at the bottom of the extent tree
>>>  typedef struct {
>>>    // First logical block
>>> diff --git a/Features/Ext4Pkg/Ext4Dxe/Extents.c b/Features/Ext4Pkg/Ext4Dxe/Extents.c
>>> index 5fa2fe0..21af573 100644
>>> --- a/Features/Ext4Pkg/Ext4Dxe/Extents.c
>>> +++ b/Features/Ext4Pkg/Ext4Dxe/Extents.c
>>> @@ -332,7 +332,7 @@ Ext4GetExtent (
>>>      return EFI_NO_MAPPING;
>>>    }
>>> 
>>> -  if (!(LogicalBlock >= Ext->ee_block && Ext->ee_block +
>>> Ext->ee_len > LogicalBlock)) {
>>> +  if (!(LogicalBlock >= Ext->ee_block && Ext->ee_block +
>>> EXTENT_REAL_LEN(Ext->ee_len) > LogicalBlock)) {
>>>      // This extent does not cover the block
>>>      if (Buffer != NULL) {
>>>        FreePool (Buffer);
>>> @@ -413,7 +413,7 @@ Ext4ExtentsMapKeyCompare (
>>>    Extent = UserStruct;
>>>    Block  = (UINT32)(UINTN)StandaloneKey;
>>> 
>>> -  if (Block >= Extent->ee_block && Block < Extent->ee_block +
>>> Extent->ee_len) {
>>> +  if (Block >= Extent->ee_block && Block < Extent->ee_block +
>>> EXTENT_REAL_LEN(Extent->ee_len)) {
>>>      return 0;
>>>    }
>>> 
>>> diff --git a/Features/Ext4Pkg/Ext4Dxe/Inode.c b/Features/Ext4Pkg/Ext4Dxe/Inode.c
>>> index 63cecec..d691ec7 100644
>>> --- a/Features/Ext4Pkg/Ext4Dxe/Inode.c
>>> +++ b/Features/Ext4Pkg/Ext4Dxe/Inode.c
>>> @@ -151,6 +151,11 @@ Ext4Read (
>>>        // Potential improvement: In the future, we could get the
>>> hole's tota
>>>        // size and memset all that
>>>        SetMem (Buffer, WasRead, 0);
>>> +    } else if(EXTENT_IS_UNWRITTEN(Extent.ee_len)) {
>>> +      HoleOff = CurrentSeek - (UINT64)Extent.ee_block * Partition->BlockSize;
>>> +      HoleLen = EXTENT_REAL_LEN(Extent.ee_len) *
>>> Partition->BlockSize - HoleOff;
>>> +      WasRead = HoleLen > RemainingRead ? RemainingRead : HoleLen;
>>> +      SetMem (Buffer, WasRead, 0);
>>>      } else {
>>>        ExtentStartBytes = MultU64x32 (
>>>                             LShiftU64 (Extent.ee_start_hi, 32) |
>>> --
>>> 2.17.1
>>> 
> 
> 
> --
> 
> Pedro Falcato