shell: add trace command

[xuchang-vivo]

Summary

• Add a trace shell command for controlling the kernel tracing subsystem through procfs.
• Register the command in the shell command table.
• Stream trace dump output in fixed-size chunks to avoid allocating the whole dump in memory.

Usage

The command expects the kernel tracing procfs ABI to be available under /proc/trace.

Start a fresh tracing session:

trace start

Stop tracing:

trace stop

Reset tracing buffers and counters:

trace reset

Print tracing status and counters:

trace stats

Print decoded trace events:

trace dump

Save the raw binary BTRC trace stream for host-side tooling:

trace dump --raw /tmp/trace.btrc

If tracing is not compiled into the kernel, the command reports that tracing is disabled in this build.

Notes

• Control commands are written to /proc/trace/control.
• Statistics are read from /proc/trace/stats.
• Decoded text output is read from /proc/trace/dump.
• Raw binary output is read from /proc/trace/raw.

Validation

• Not rerun while creating this PR.
• This shell command is intended to be validated with the matching kernel tracing PR using qemu_mps2_an385.debug and shell_runner.