zdb raidz file layout

[don-brady]

Motivation and Context

It would be nice to be able to visualize how the RAIDZ disk columns for a given file are laid out on disk. For example, one might ponder if the parity is being evenly distributed or are the same disks being used for parity?

Description

This change introduces the --file-layout (-f) option to zdb(8) to display the raidz file layout for a given file. The change leverages the vdev_raidz_map_alloc() function to find the map of how the block data is laid out across the child disks.

A typical column entry looks like:

┌────────────┐
│  D2     43 │
│     6020da │
└────────────┘

Which here represents the logical data column 2 that is 43 sectors high starting at sector 0x6020da. The parity is displayed in inverse text if output is to a terminal (see example below).

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.

An example

How Has This Been Tested?

Tested with various flavors of raidz and disk counts.
Tested with ZTS cli_root/zdb suite of tests.

Known Issues/Limitations

1. Only supports RAIDZ. A follow-on pull request can add support for dRAID.
2. The check for the last row is not always correct and so the edge connector, like '├', can sometimes show final connector '└' by mistake.
3. Only supports one top-level RAIDZ

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[tonyhutter]

I just tested this by printing out different objects. Seems to work fine:

$ sudo ./zdb -f tank/dir1 36
      objset: 'tank/dir1'
      object: 36
  block size: 16384
   vdev_type: raidz1
 sector size: 512
 child disks: 3

               V0:DISK-0   V0:DISK-1   V0:DISK-2 
 FILE OFFSET ┌────────────────────────────────────┐
           0 │ ` ` ` ` `    P0     16   D0     16 │
             │  ` ` ` ` `       4cb0f       4cb0f │
             │  D1     16  ` ` ` ` `   ` ` ` ` `  │
             │      4cb10   ` ` ` ` `   ` ` ` ` ` │
             └────────────────────────────────────┘
        4000 │ ` ` ` ` `   ` ` ` ` `    P0     16 │
             │  ` ` ` ` `   ` ` ` ` `       4cb0a │
             │  D0     16   D1     16  ` ` ` ` `  │
             │      4cb0b       4cb0b   ` ` ` ` ` │
             └────────────────────────────────────┘

The scripted mode columns don't align with the values, but I don't know if that matters since it's scripted mode:

$ sudo ./zdb -Hf tank/dir1 36
      objset: 'tank/dir1'
      object: 36
DISK		LBA		COUNT
file2	314127	16
file3	314127	16
file1	314128	16
file3	314122	16
file1	314123	16
file2	314123	16

Some of the edge cases have ASCII art a little off, but again, I don't think it matters:

Empty or small file:

$ sudo ./zdb -f tank/dir1 2
      objset: 'tank/dir1'
      object: 2
  block size: 512
   vdev_type: raidz1
 sector size: 512
 child disks: 3

               V0:DISK-0   V0:DISK-1   V0:DISK-2 
 FILE OFFSET ┌────────────────────────────────────┐

$

Printing out the "ZFS Master node" for a dataset:

$ sudo ./zdb -v  -d tank/dir1
...
         1    1   128K    512  1.50K     512    512  100.00  ZFS master node
...
$ sudo ./zdb -f tank/dir1 1
      objset: 'tank/dir1'
      object: 1
  block size: 512
   vdev_type: raidz1
 sector size: 512
 child disks: 3

               V0:DISK-0   V0:DISK-1   V0:DISK-2 
 FILE OFFSET ┌────────────────────────────────────┐
           0 │ ` ` ` ` `   ` ` ` ` `    P0      1 │
             │  ` ` ` ` `   ` ` ` ` `       4cad8 │
             │  D0      1 │
             │      4cad9 │
             ├────────────────────────────────────┤

[tonyhutter]

Might want to add in your commit message that -d also prints this header now.

[tonyhutter]

Might want to mention -H here, like:

Display the file layout of an object for the disks of a raidz vdev.
You can optionally pass -H to print the file layout in scripted mode for easy parsing.