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
