Thanks for your help. I'm afraid I'm still confused somehow about this.
>> If the handler successfully completes execution of the block I/O command
>> in the callout function, what TCMU_STS code should it return from the
>> callout function
>
> What is says on line 128.
>
> You must return a TCMU_STS code. It can TMCU_STS_OK or a TCMU_STS error
> value like TCMU_STS_WR_ERR.
So, then, line 137 is intended to apply only to line 131 and not line 128?
I was reading it as applying to both.
> For handlers like file_example that operate like described on line 128,
> tcmu-runner core will do cmd->done for it.
If TCMU_STS_OK is returned from file_read(), how does runner know whether that is
(1) TCMU_STS_OK because the handler is async and it queued the command, and
there will be a future call to tcmur_cmd_complete() from the handler; or
(2) TCMU_STS_OK because the handler executed the entire command successfully
and runner needs to issue the cmd->done for it now?
Also, I wonder why the return from async handlers for successful queueing
of the command is TCMU_STS_OK rather than TCMU_STS_ASYNC_HANDLED.
>> 125 /*
>> 126 * Below callouts are only executed by generic_handle_cmd.
>> 127 *
>> 128 * Handlers that completely execute cmds from the callout's calling
>> 129 * context must return a TCMU_STS code from the callout.
>> 130 *
>> 131 * Async handlers that queue a command from the callout and complete
>> 132 * it from their own async context return:
>> 133 * - TCMU_STS_OK if the handler has queued the command.
>> 134 * - TCMU_STS_NO_RESOURCE if the handler was not able to allocate
>> 135 * resources to queue the command.
>> 136 *
>> 137 * If TCMU_STS_OK is returned from the callout the handler must call
>> 138 * tcmur_cmd_complete with a TCMU_STS return code to complete the
>> 139 * command.
>> 140 */
>> 141 int (*read)(struct tcmu_device *dev, struct tcmur_cmd *cmd,
>> 142 struct iovec *iovec, size_t iov_cnt, size_t len, off_t off);
>> 143 int (*write)(struct tcmu_device *dev, struct tcmur_cmd *cmd,
>> 144 struct iovec *iovec, size_t iov_cnt, size_t len, off_t off);
>> 145 int (*flush)(struct tcmu_device *dev, struct tcmur_cmd *cmd);
