[PATCH 1/3] fio: Fix error string not matching errno

[Niklas Cassel <cassel@kernel.org>]

When using --error_dump=1 together with --continue_on_error=io and
--ignore_error=62, we can get an inconsistent error in the summary line
 produced by __show_run_stats():

Before patch:
test: (groupid=0, jobs=1): err= 5 (file:io_u.c:2012, func=io_u error, error=Timer expired): pid=30925: Thu Feb  5 09:15:15 2026
...
  IO depths    : 1=0.8%, 2=1.6%, 4=3.3%, 8=6.6%, 16=13.1%, 32=74.6%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=98.9%, 8=0.0%, 16=0.0%, 32=1.1%, 64=0.0%, >=64=0.0%
     issued rwts: total=0,122,0,0 short=0,0,0,0 dropped=0,0,0,0
     errors    : total=4, first_error=62/<Timer expired>
     latency   : target=0, window=0, percentile=100.00%, depth=32

The string for errno "err= 5" is incorrectly printed as "Timer expired".
(The correct string for "err= 5" is "Input/output error".)

There is thus a mismatch between the errno and the verbose string for the
errno.

This problem is this code in __td_verror():

td->error = ____e;
if (!td->first_error)
	nowarn_snprintf(td->verror, ..);

I.e. td->error (errno) is updated unconditionally, while td->verror (the
verbose error string), is updated only if td->first_error is not set.

Thus, if you get a non-fatal error, it will set td->error and td->error.
Later, for a non-fatal error, io_completed() will call update_error_count()
which sets td->first_error, followed by td_clear_error() which will clear
td->error.

Thus a second error (fatal or non-fatal) will set td->error, but since
td->first_error is now set, it will not update td->verror.

Since td->verror contains the string representation of the errno stored in
td->error, these two struct members should obviously always be updated at
the same time.

If you look at the example print above, you can see that there is another
print: first_error=62/<Timer expired>

Which prints td->first_error, and does not even use td->verror. Instead
show_thread_status_normal() calls strerror(td->first_error) to get the
error string for td->first_error.

There is thus absolutely no reason to not set td->verror every time
td->error is set.

Remove the useless guard such that the error string will always correspond
to errno.

Fixes: f2bba1820a56 ("Add a 'continue_on_error' option to fio")
Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
 fio.h | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/fio.h b/fio.h
index e0b7c13c..65c68d4b 100644
--- a/fio.h
+++ b/fio.h
@@ -542,10 +542,9 @@ enum {
 		if ((td)->error)					\
 			break;						\
 		(td)->error = ____e;					\
-		if (!(td)->first_error)					\
-			nowarn_snprintf(td->verror, sizeof(td->verror),	\
-					"file:%s:%d, func=%s, error=%s", \
-					__FILE__, __LINE__, (func), (msg)); \
+		nowarn_snprintf(td->verror, sizeof(td->verror),		\
+				"file:%s:%d, func=%s, error=%s",	\
+				__FILE__, __LINE__, (func), (msg));	\
 	} while (0)
 
 
-- 
2.53.0