On 08/08/2019 12:50 AM, David Butterfield wrote: > 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? Correct. > 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 handl> > (2) TCMU_STS_OK because the handler executed the entire command successfully > and runner needs to issue the cmd->done for it now? If you set nr_threads > 0 and implement the callouts below then TCMU_STS_OK means you completed the command in the callout successfully. If you set nr_threads = 0 and implement the callouts below then OK means it got queued successfully and the handler is going to complete it by calling tcmur_cmd_complete. We do not have any handlers where nr_threads = 0, the callouts below are implemented and the handler executes the command in the callout, so it's not supported right 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. It's just one of those things that needs to be cleaned up. tcmu-runner uses it internally and when interacting with libtcmu, and runner handlers that only implement a handle_cmd can use it directly. > >>> 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); >
