Re: [PATCH 0/4] migration: Replace gemu_log with qemu_log

[Warner Losh <imp@bsdimp.com>]

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On Mon, Jan 13, 2020, 8:03 PM Josh Kunz <jkz@google.com> wrote:

> The linux-user and bsd-user trees both widely use a function called
> `gemu_log` (notice the 'g') for miscellaneous and strace logging. This
> function predates the newer `qemu_log` function, and has a few drawbacks
> compared to `qemu_log`:
>
>   1. Always logs to `stderr`, no logging redirection.
>   2. "Miscellaneous" logging cannot be disabled, so it may mix with guest
>      logging.
>   3. Inconsistency with other parts of the QEMU codebase, and a
>      confusing name.
>
> The second issue is especially troubling because it can interfere with
> programs that expect to communicate via stderr.
>
> This change introduces two new logging masks to the `qemu_log` subsystem
> to support its use for user-mode logging. The `LOG_USER` mask, for
> miscellaneous logs, and the `LOG_STRACE` mask for strace-specific
> logging. Further, it replaces all existing uses of `gemu_log` with the
> appropriate `qemu_log_mask(LOG_{USER,STRACE}, ...)` based on the log
> message. To avoid potential backwards incompatibility, this patch series
> also introduces a new flag: `-no-force-user-mode-logging`. Since "user
> mode" logging was always enabled before this change, by-default the
> LOG_USER mask is always set. The flag is provided for users that want to
> disable LOG_USER. Hopefully, this flag can be removed, or turned into a
> no-op in the futre, and -d/QEMU_LOG can be used directly to enable
> user-mode logging if desired.
>
> Unfortunately, this change introduces one small backwards incompatibility
> for the linux-user tree: If an explicit `-D` option is provided, or the
> `QEMU_LOG_FILENAME`_ environment variable is set, strace and user-mode
> logging statements will log to the QEMU log file instead of stderr.
>
> Tested:
>   * Built with clang 9 and g++ 8.3
>   * `make check` run with clang 9 build
>   * Verified:
>     * QEMU_STRACE/-strace still works for linux-user
>     * -no-force-user-mode-logging uses QEMU_LOG + `user_mode` or
>       `strace` can be set in QEMU_LOG to trigger the appropriate
>       logging.
>
> Not tested:
>   * Build/logging with bsd-user. I do not have easy access to a BSD system.
>

The bsd-user that is in tree doesn't work. I've been trying to catch up to
qemu head of tree, but I'm only up to 3.2... chances are the bsd-user
changes will not change the state of things...

Warner

Josh Kunz (4):
>   linux-user: Use `qemu_log' for non-strace logging
>   linux-user: Use `qemu_log' for strace
>   linux-user: remove gemu_log from the linux-user tree
>   bsd-user: Replace gemu_log with qemu_log
>
>  bsd-user/main.c           |  13 +-
>  bsd-user/qemu.h           |   2 -
>  bsd-user/strace.c         |  32 ++-
>  bsd-user/syscall.c        |  31 ++-
>  include/qemu/log.h        |  15 ++
>  linux-user/arm/cpu_loop.c |   5 +-
>  linux-user/fd-trans.c     |  55 +++--
>  linux-user/main.c         |  50 +++-
>  linux-user/qemu.h         |   2 -
>  linux-user/signal.c       |   3 +-
>  linux-user/strace.c       | 479 +++++++++++++++++++-------------------
>  linux-user/syscall.c      |  43 ++--
>  linux-user/vm86.c         |   3 +-
>  util/log.c                |   5 +
>  14 files changed, 404 insertions(+), 334 deletions(-)
>
> --
> 2.25.0.rc1.283.g88dfdc4193-goog
>
>
>

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