On 8/1/19 10:18 AM, Mike Christie wrote:
> Update your tcmu-runner git repo :)
>
> A little bit ago, the comments in tcmu-runner.h were updated to make it
> clear what type of handler can do what, and also support for not having
> to call cmd->done in handlers like file_example was added.
I've pulled the latest master and the comment has been revised, but part
of my question still remains:
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?
It can't be TCMU_STS_OK, right? Because that would leave tcmu-runner
expecting a call to cmd->done() later.
And it can't be a TCMU_STS error, because the I/O was successful.
So what does the handler return to indicate both success and completion?
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);
>> However, the code in file_example.c does not do either of those things, and directly
>> violates the comment in tcmu-runner.h -- this excerpt is from file_read():
>>
>> while (remaining) {
>> ret = preadv(state->fd, iov, iov_cnt, offset);
>> if (ret < 0) {
>> tcmu_err("read failed: %m\n");
>> ret = TCMU_STS_RD_ERR;
>> goto done;
>> }
>> ...
>> }
>> ret = TCMU_STS_OK;
>> done:
>> return ret;
>>
>> The file_read() function operates synchronously, and never issues a call to cmd->done()
>> for successful reads returning TCMU_STS_OK, contradicting the comment in tcmu-runner.h.
