Re: [edk2-devel] [edk2-platforms PATCH] Ext4Pkg: Add uninitialized extents support

["Pedro Falcato" <pedro.falcato@gmail.com>]

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Quick PS: I CC'd the edk2-platforms stewards on the patch because there's
no co-maintainer, and from what I gathered, that's what I'm supposed to do.
If I'm mistaken, please let me know.

Thanks,
Pedro

On Fri, Oct 29, 2021 at 2:04 AM Pedro Falcato via groups.io <pedro.falcato=
gmail.com@groups.io> wrote:

> Uninitialized extents are special extents that have blocks allocated,
> but are specified as uninitialized and therefore, reads behave the
> same as file holes (reads 0), while writes already have blocks allocated.
>
> Cc: Leif Lindholm <leif@nuviainc.com>
> Cc: Michael D Kinney <michael.d.kinney@intel.com>
> Signed-off-by: Pedro Falcato <pedro.falcato@gmail.com>
> ---
>  Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h |  8 ++++++++
>  Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h  | 21 +++++++++++++++++++++
>  Features/Ext4Pkg/Ext4Dxe/Extents.c  | 24 ++++++++++++++++++++++--
>  Features/Ext4Pkg/Ext4Dxe/Inode.c    | 14 +++++++++++---
>  4 files changed, 62 insertions(+), 5 deletions(-)
>
> diff --git a/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
> b/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
> index 070eb5a9c8..756b1bbe10 100644
> --- a/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
> +++ b/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
> @@ -448,6 +448,14 @@ typedef struct {
>    UINT32    eb_checksum;
>  } EXT4_EXTENT_TAIL;
>
> +/**
> + * EXT4 has this feature called uninitialized extents:
> + * An extent has a maximum of 32768 blocks (2^15 or 1 << 15).
> + * When we find an extent with > 32768 blocks, this extent is called
> uninitialized.
> + * Long story short, it's an extent that behaves as a file hole but has
> blocks already allocated.
> + */
> +#define EXT4_EXTENT_MAX_INITIALIZED  (1 << 15)
> +
>  typedef UINT64  EXT4_BLOCK_NR;
>  typedef UINT32  EXT4_INO_NR;
>
> diff --git a/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
> b/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
> index a9b932ed52..1d9a4ac6ba 100644
> --- a/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
> +++ b/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
> @@ -1131,4 +1131,25 @@ Ext4SuperblockCheckMagic (
>    IN EFI_BLOCK_IO_PROTOCOL  *BlockIo
>    );
>
> +/**
> +   Check if the extent is uninitialized
> +
> +   @param[in] Extent    Pointer to the EXT4_EXTENT
> +
> +   @returns True if uninitialized, else false.
> +**/
> +#define EXT4_EXTENT_IS_UNINITIALIZED(Extent) ((Extent)->ee_len >
> EXT4_EXTENT_MAX_INITIALIZED)
> +
> +/**
> +   Retrieves the extent's length, dealing with uninitialized extents in
> the process.
> +
> +   @param[in] Extent      Pointer to the EXT4_EXTENT
> +
> +   @returns Extent's length, in filesystem blocks.
> +**/
> +EXT4_BLOCK_NR
> +Ext4GetExtentLength (
> +  IN CONST EXT4_EXTENT  *Extent
> +  );
> +
>  #endif
> diff --git a/Features/Ext4Pkg/Ext4Dxe/Extents.c
> b/Features/Ext4Pkg/Ext4Dxe/Extents.c
> index 5fa2fe098d..1ae175f417 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 +
> Ext4GetExtentLength (Ext) > 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 +
> Ext4GetExtentLength (Extent)) {
>      return 0;
>    }
>
> @@ -593,3 +593,23 @@ Ext4CheckExtentChecksum (
>
>    return Tail->eb_checksum == Ext4CalculateExtentChecksum (ExtHeader,
> File);
>  }
> +
> +/**
> +   Retrieves the extent's length, dealing with uninitialized extents in
> the process.
> +
> +   @param[in] Extent      Pointer to the EXT4_EXTENT
> +
> +   @returns Extent's length, in filesystem blocks.
> +**/
> +EXT4_BLOCK_NR
> +Ext4GetExtentLength (
> +  IN CONST EXT4_EXTENT  *Extent
> +  )
> +{
> +  // If it's an unintialized extent, the true length is ee_len - 2^15
> +  if (EXT4_EXTENT_IS_UNINITIALIZED (Extent)) {
> +    return Extent->ee_len - EXT4_EXTENT_MAX_INITIALIZED;
> +  }
> +
> +  return Extent->ee_len;
> +}
> diff --git a/Features/Ext4Pkg/Ext4Dxe/Inode.c
> b/Features/Ext4Pkg/Ext4Dxe/Inode.c
> index 63cecec1f7..48bfe026a3 100644
> --- a/Features/Ext4Pkg/Ext4Dxe/Inode.c
> +++ b/Features/Ext4Pkg/Ext4Dxe/Inode.c
> @@ -144,11 +144,19 @@ Ext4Read (
>
>      HasBackingExtent = Status != EFI_NO_MAPPING;
>
> -    if (!HasBackingExtent) {
> +    if (!HasBackingExtent || EXT4_EXTENT_IS_UNINITIALIZED (&Extent)) {
> +
>        HoleOff = BlockOff;
> -      HoleLen = Partition->BlockSize - HoleOff;
> +
> +      if (!HasBackingExtent) {
> +        HoleLen = Partition->BlockSize - HoleOff;
> +      } else {
> +        // Uninitialized extents behave exactly the same as file holes.
> +        HoleLen = Ext4GetExtentLength (&Extent) - HoleOff;
> +      }
> +
>        WasRead = HoleLen > RemainingRead ? RemainingRead : HoleLen;
> -      // Potential improvement: In the future, we could get the hole's
> tota
> +      // Potential improvement: In the future, we could get the file
> hole's total
>        // size and memset all that
>        SetMem (Buffer, WasRead, 0);
>      } else {
> --
> 2.33.1.windows.1
>
>
>
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> ------------
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>
>

-- 
Pedro Falcato

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