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Log to stderr by default. (#1266)

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Change the default from file-per-thread-logger to pretty-env-logger,
which is more common in Rust projects, and change the option from `-d`
to `--log-to-files`.
This commit is contained in:
Dan Gohman
2020-03-10 07:36:56 -07:00
committed by GitHub
parent 674a6208d8
commit ac0ee271b1
6 changed files with 40 additions and 14 deletions
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docs/cli-logging.md Normal file
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# Logging in the `wasmtime` CLI
Wasmtime's libraries use Rust's [`log`] crate to log diagnostic
information, and the `wasmtime` CLI executable uses [`pretty_env_logger`]
by default for logging this information to the console.
Basic logging is controlled by the `RUST_LOG` environment variable. For example,
To enable logging of WASI system calls, similar to the `strace` command on Linux,
set `RUST_LOG=wasi_common=trace`.
```sh
$ RUST_LOG=wasi_common=trace wasmtime hello.wasm
[...]
TRACE wasi_common::hostcalls_impl::fs > fd_write(fd=1, iovs_ptr=0x10408, iovs_len=1, nwritten=0x10404)
Hello, world!
TRACE wasi_common::hostcalls_impl::fs > | *nwritten=14
TRACE wasi_common::hostcalls > | errno=ESUCCESS (No error occurred. System call completed successfully.)
TRACE wasi_common::hostcalls_impl::misc > proc_exit(rval=1)
```
Wasmtime can also redirect the log messages into log files, with the
`--log-to-files` option. It creates one file per thread within Wasmtime, with
the files named `wasmtime.dbg.*`.
[`log`]: https://crates.io/crates/log
[`pretty_env_logger`]: https://crates.io/crates/pretty_env_logger