doc lsblk usage

docs/usage/commands/lsblk.md

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+# lsblk
+
+`lsblk` lists the block devices detected by BoredOS, including whole disks and their partitions.
+
+## Usage
+
+```sh
+lsblk
+lsblk /dev/sda
+lsblk -r
+lsblk --json
+```
+
+## Output
+
+By default, `lsblk` prints a compact tree view:
+
+```text
+/dev/sda       2 GB  disk
+└─ sda1        2 GB  part  FAT32  BOREDOS
+```
+
+Fields shown by the default output:
+
+- device name, such as `/dev/sda` or `sda1`
+- human-readable size, such as `512 MB` or `2 GB`
+- device type, either `disk` or `part`
+- filesystem type, currently `FAT32` when detected
+- volume label when available
+- `[ESP]` flag for EFI System Partitions
+
+> [!NOTE]
+> Mount points are not shown yet because BoredOS does not currently expose mountpoint information through the disk info syscall.
+
+## Options
+
+| Option | Description |
+| :--- | :--- |
+| `-r` | Print raw output without tree characters. |
+| `--json` | Print machine-readable JSON output. |
+| `/dev/DEVICE` | Show only one disk or partition. |
+
+## Examples
+
+List all block devices:
+
+```sh
+lsblk
+```
+
+Example output:
+
+```text
+/dev/sda       2 GB  disk
+└─ sda1        2 GB  part  FAT32  BOREDOS
+/dev/sdb      16 GB  disk
+```
+
+Show one disk and its partitions:
+
+```sh
+lsblk /dev/sda
+```
+
+Example output:
+
+```text
+/dev/sda       2 GB  disk
+└─ sda1        2 GB  part  FAT32  BOREDOS
+```
+
+Print raw output for scripts:
+
+```sh
+lsblk -r
+```
+
+Example output:
+
+```text
+/dev/sda 2GB disk
+/dev/sda1 2GB part FAT32 BOREDOS
+```
+
+Print JSON output:
+
+```sh
+lsblk --json
+```
+
+Example output:
+
+```json
+{"devices":[{"name":"/dev/sda","size":"2 GB","type":"disk","fstype":"","label":"","flags":[],"children":[{"name":"/dev/sda1","size":"2 GB","type":"part","fstype":"FAT32","label":"BOREDOS","flags":[]}]}]}
+```
+
+## How It Works
+
+`lsblk` reads disk metadata through the disk syscalls exposed by BoredOS:
+
+- `sys_disk_get_count()` gets the number of registered block devices.
+- `sys_disk_get_info()` reads each device's name, size, type, FAT32 status, label, and flags.
+
+The command treats non-partition entries as parent disks, then groups partition entries under the matching disk name. For example, `sda1` is displayed under `/dev/sda`.
+
+Sizes are calculated from sector counts using 512-byte sectors, then formatted as `KB`, `MB`, or `GB`.