On Tue, 29 Jun 2010 09:22:12 -0700 Joe Eykholt <jeykholt@xxxxxxxxx> wrote: > >> My specific question at this point deals with how the kernel > >> knows the status of a WRITE command. > >> > >> My guess is that for WRITEs, the user-kernel interactions are: > >> > >> 1. TGT_KEVENT_CMD_REQ - kernel presents command to tgtd. > >> 2. TGT_UEVENT_CMD_RSP - tgtd gives buffer address to kernel > >> - send XFER_RDY > >> - kernel fills in buffer > >> 3. TGT_KEVENT_CMD_DONE - kernel indicates write data in buffer > >> > >> .... then, what tells the kernel it's safe to send the response? > >> If we do it between 2 and 3, then the data isn't really safe yet. > >> Is there another TGT_UEVENT_CMD_RSP? > > > > You mean that the data might not be committed to disk persistently? > > Yes. If the system were to crash just after the response was sent, > the data might be lost. > > So, it seems we should modify the interactions to have one to > say "get the data" between 1 and 2, or something like that. Adding an interaction between kernel and user space increases latency. scsi_cmnd includes the information about all the pages so the llds can see if the data is committed or not? -- To unsubscribe from this list: send the line "unsubscribe stgt" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
