Handle interrupts in __ublksrv_ctrl_cmd #79
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The syscall io_uring_enter may return EINTR if it is interrupted by a delivery of a signal. Since __ublksrv_ctrl_cmd already added an SQE, it's easier for ublksrv to handle the error instead of the caller. For example, if ublksrv_ctrl_start_dev() returns -EINTR, then the caller has to either manually wait for the CQE or might call ublksrv_ctrl_start_dev() again, resulting in an erroneous second SQE. (Which may have no effect, but handling the interrupt seems the most correct)
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The syscall
io_uring_entermay return EINTR if it is interrupted by a delivery of a signal. This was happening to me recently; I saw that theSIG_PROFsignal fired periodically, which would fail theublksrv_ctrl_start_dev()call (returns -EINTR). The signal is firing due to unrelated circumstances.Since __ublksrv_ctrl_cmd already added an SQE, it's easier for ublksrv to handle the error instead of the caller.
Note that I only added support to
__ublksrv_ctrl_cmdsince control commands are likely to be done once on startup. io_urings for handling IO are already expected to loop for IO, so there's no need for ublksrv to explicitly handle theEINTR.Currently the code loops indefinitely. I'm also considering it best practice to set some maximum retry number or timeout, but I wanted to get your opinion first.
Also I thought about using
TEMP_FAILURE_RETRYbut the semantics fromio_uring_wait_cqeare a bit different.TEMP_FAILURE_RETRYexpects the return code to be-1and then checkserrno, butio_uring_wait_cqereturns -EINTR directly, so the do while loop is necessary.