Add man docs for return values indicating a CQE was lost. Signed-off-by: Dylan Yudaken <dylany@xxxxxx> --- man/io_uring_enter.2 | 11 +++++++++++ man/io_uring_setup.2 | 11 +++++++++-- 2 files changed, 20 insertions(+), 2 deletions(-) diff --git a/man/io_uring_enter.2 b/man/io_uring_enter.2 index 9ad6349b2c4a..688e57984f00 100644 --- a/man/io_uring_enter.2 +++ b/man/io_uring_enter.2 @@ -1326,6 +1326,17 @@ is a valid file descriptor, but the io_uring ring is not in the right state .BR io_uring_register (2) for details on how to enable the ring. .TP +.B EBADR +At least one CQE was dropped even with the +.B IORING_FEAT_NODROP +feature, and there are no otherwise available CQEs. This clears the error state +and so with no other changes the next call to +.BR io_uring_setup (2) +will not have this error. This error should be extremely rare and indicates the +machine is running critically low on memory and. It may be reasonable for the +application to terminate running unless it is able to safely handle any CQE +being lost. +.TP .B EBUSY If the .B IORING_FEAT_NODROP diff --git a/man/io_uring_setup.2 b/man/io_uring_setup.2 index 0f57d8f06a35..9a543d68dd02 100644 --- a/man/io_uring_setup.2 +++ b/man/io_uring_setup.2 @@ -279,7 +279,7 @@ call. The SQEs must still be allocated separately. This brings the necessary calls down from three to two. Available since kernel 5.4. .TP .B IORING_FEAT_NODROP -If this flag is set, io_uring supports never dropping completion events. +If this flag is set, io_uring supports almost never dropping completion events. If a completion event occurs and the CQ ring is full, the kernel stores the event internally until such a time that the CQ ring has room for more entries. If this overflow condition is entered, attempting to submit more @@ -287,7 +287,14 @@ IO will fail with the .B -EBUSY error value, if it can't flush the overflown events to the CQ ring. If this happens, the application must reap events from the CQ ring and attempt the -submit again. Available since kernel 5.5. +submit again. If the kernel has no free memory to store the event internally +it will be visible by an increase in the overflow value on the cqring. +Available since kernel 5.5. Additionally +.BR io_uring_enter (2) +will return +.B -EBADR +the next time it would otherwise sleep waiting for completions (since kernel 5.19). + .TP .B IORING_FEAT_SUBMIT_STABLE If this flag is set, applications can be certain that any data for -- 2.30.2
