[PATCH v5 00/24] util: sync error_report & qemu_log output more closely

This series is a tangent that came out of discussion in

   https://lists.nongnu.org/archive/html/qemu-devel/2025-08/msg00903.html

In thinking about adding thread info to error_report, I
came to realize we should likely make qemu_log behave
consistently with error_report & friends. We already
honour '-msg timestamp=on', but don't honour 'guest-name=on'
and also don't include the binary name.

As an example of the current state, consider mixing error and
log output today:

- Default context:

  # qemu-system-x86_64 -object tls-creds-x509,id=t0,dir=fish \
                       -d 'trace:qcrypto*'
  qcrypto_tls_creds_x509_load TLS creds x509 load creds=0x55ac6d97f700 dir=fish
  qcrypto_tls_creds_get_path TLS creds path creds=0x55ac6d97f700 filename=ca-cert.pem path=<none>
  qemu-system-x86_64: Unable to access credentials fish/ca-cert.pem: No such file or directory

- Full context:

  # qemu-system-x86_64 -object tls-creds-x509,id=t0,dir=fish \
                       -d 'trace:qcrypto*' \
                       -msg guest-name=on,timestamp=on \
                       -name "fish food"
  2025-08-19T20:14:16.791413Z qcrypto_tls_creds_x509_load TLS creds x509 load creds=0x55e9a3458d10 dir=fish
  2025-08-19T20:14:16.791429Z qcrypto_tls_creds_get_path TLS creds path creds=0x55e9a3458d10 filename=ca-cert.pem path=<none>
  2025-08-19T20:14:16.791433Z fish food qemu-system-x86_64: Unable to access credentials fish/ca-cert.pem: No such file or directory

And after this series is complete:

- Default context:

  # qemu-system-x86_64 -object tls-creds-x509,id=t0,dir=fish \
                      -d 'trace:qcrypto*'
  qemu-system-x86_64(1184284:main): qcrypto_tls_creds_x509_load TLS creds x509 load creds=0x55a24ad5cb30 dir=fish
  qemu-system-x86_64(1184284:main): qcrypto_tls_creds_get_path TLS creds path creds=0x55a24ad5cb30 filename=ca-cert.pem path=<none>
  qemu-system-x86_64(1184284:main): Unable to access credentials fish/ca-cert.pem: No such file or directory

- Full context:

  # qemu-system-x86_64 -object tls-creds-x509,id=t0,dir=fish \
                      -d 'trace:qcrypto*' \
                      -msg guest-name=on,timestamp=on \
                      -name "fish food"
  2025-08-19T20:12:50.211823Z [fish food] qemu-system-x86_64(1168876:main): qcrypto_tls_creds_x509_load TLS creds x509 load creds=0x5582183d8760 dir=fish
  2025-08-19T20:12:50.211842Z [fish food] qemu-system-x86_64(1168876:main): qcrypto_tls_creds_get_path TLS creds path creds=0x5582183d8760 filename=ca-cert.pem
+path=<none>
  2025-08-19T20:12:50.211846Z [fish food] qemu-system-x86_64(1168876:main): Unable to access credentials fish/ca-cert.pem: No such file or directory

The main things to note:

 * error_report/warn_report/qemu_log share the same
   output format and -msg applies to both

 * -msg debug-threads=on is now unconditionally enabled
   and thus the param is deprecated & ignored

 * Thread ID and name are unconditionally enabled

 * Guest name is surrounded in [...] brackets

 * The default output lines are typically 15 chars
   wider given that we always include the thread
   ID + name now

 * This takes the liberty of assigning the new file
   to the existing error-report.c maintainer (Markus)
   Since splitting it off into message.c instead of
   putting it all in error-report.c felt slightly
   nicer.

One thing I didn't tackle is making the location
info get reported for qemu_log. This is used to
give context for error messages when parsing some
CLI args, and could be interesting for log messages
associated with those same CLI args.

Changes in v5:

 - Remove redundant [] around values in qemu-options.hx
 - Use g_strlcpy instead of strlcpy
 - Remove redundant !! around a value that was already bool
 - Improve the qemu_lock_trylock() API docs to encourage
   use of fprintf() instead of further qemu_log() calls
 - Add a qemu_log_trylock_context() counterpart for
   qemu_log_trylock that includes the message context
 - Don't scan for \n to determine whether we can output
   a message context prefix or not. Instead track call
   depth on qemu_log_trylock() and only output it when
   the depth was initially zero. This fixes linux-user
   -strace output formatting which was mangled by v4
 - Use fprintf(stderr) instead of error_printf_mon
   in cases where mon would be NULL
 - Use fputs/fputc in simple cases where we don't need the
   full power of fprintf
 - Use qemu_f{un}lockfile instead of f{un}lockfile
 - Add  -msg thread-info=on|off,program-name=on|off args
   to allow default message prefixes to be optionally disabled

Changes in v4:

 - Re-architected the way error_vprintf() operates
   to simplify monitor dependency
 - Fixed the move of error_vprintf from monitor.c
   to error-report.c so that unit tests can still
   get a stub to capture messages to g_test_message
 - Simplify changes to vreport() to avoid passing
   around function pointers
 - Add locking of stderr to vreport() to serialize
   incremental output
 - Fix thread naming logic changes on Windows
 - Change deprecation warning messages

Changes in v3:

 - Stop formatting a string in qmessage_context, instead
   output directly to a "FILE *" stream
 - Fix pre-existing bug interleaving qemu_log and
   vreport when the trace 'log' backend has mutex probes
   enabled

Changes in v2:

 - Re-use existing qemu_get_thread_id rather than
   re-inventing it as qemu_thread_get_id.
 - Expose qemu_thread_set_name and use it from all
   locations needing to set thread names
 - Fix qemu_log() to skip context prefix when
   emitting a log message in fragments across
   multiple calls
 - Skip allocating memory for empty context messages
 - Fix leak in win32 impl of qemu_thread_get_name
 - Use g_strlcpy where possible

Daniel P. Berrangé (24):
  qemu-options: remove extraneous [] around arg values
  include: define constant for early constructor priority
  monitor: initialize global data from a constructor
  system: unconditionally enable thread naming
  util: expose qemu_thread_set_name
  audio: make jackaudio use qemu_thread_set_name
  util: set the name for the 'main' thread
  util: add API to fetch the current thread name
  util: introduce some API docs for logging APIs
  util: avoid repeated prefix on incremental qemu_log calls
  ui/vnc: remove use of error_printf_unless_qmp()
  monitor: remove redundant error_[v]printf_unless_qmp
  monitor: refactor error_vprintf()
  monitor: move error_vprintf back to error-report.c
  monitor: introduce monitor_cur_is_hmp() helper
  util: don't skip error prefixes when QMP is active
  util: fix interleaving of error & trace output
  util: fix interleaving of error prefixes
  util: introduce common helper for error-report & log code
  util: convert error-report & log to message API for timestamp
  util: add support for formatting a workload name in messages
  util: add support for formatting a program name in messages
  util: add support for formatting thread info in messages
  util: add brackets around guest name in message context

 MAINTAINERS                          |   2 +
 audio/jackaudio.c                    |  30 +++++--
 docs/about/deprecated.rst            |   7 ++
 include/monitor/monitor.h            |   4 +-
 include/qemu/compiler.h              |   8 ++
 include/qemu/error-report.h          |   4 -
 include/qemu/log-for-trace.h         |  17 +++-
 include/qemu/log.h                   |  38 +++++++++
 include/qemu/message.h               |  40 +++++++++
 include/qemu/thread.h                |   3 +-
 meson.build                          |  21 +++++
 monitor/monitor.c                    |  61 +++++---------
 qemu-options.hx                      | 121 ++++++++++++++-------------
 rust/util/src/log.rs                 |   6 ++
 storage-daemon/qemu-storage-daemon.c |   6 ++
 stubs/error-printf.c                 |  23 -----
 stubs/meson.build                    |   1 -
 stubs/monitor-core.c                 |  20 ++++-
 system/vl.c                          |  49 +++++++++--
 tests/qemu-iotests/041               |   2 +-
 tests/qemu-iotests/common.filter     |   2 +-
 tests/unit/test-error-report.c       |   6 +-
 tests/unit/test-util-sockets.c       |   1 +
 ui/vnc.c                             |  14 ++--
 util/error-report.c                  |  97 ++++++++++++---------
 util/log.c                           |  47 ++++++-----
 util/meson.build                     |   1 +
 util/message.c                       |  51 +++++++++++
 util/qemu-thread-posix.c             |  77 +++++++++++------
 util/qemu-thread-win32.c             |  87 +++++++++++++------
 30 files changed, 580 insertions(+), 266 deletions(-)
 create mode 100644 include/qemu/message.h
 delete mode 100644 stubs/error-printf.c
 create mode 100644 util/message.c

-- 
2.52.0