On 3/12/21 12:53 AM, michael.christie@xxxxxxxxxx wrote: > On 2/22/21 7:23 AM, Hannes Reinecke wrote: >> Hi all, >> >> quite some drivers use internal commands for various purposes, most >> commonly sending TMFs or querying the HBA status. >> While these commands use the same submission mechanism than normal >> I/O commands, they will not be counted as outstanding commands, >> requiring those drivers to implement their own mechanism to figure >> out outstanding commands. >> The block layer already has the concept of 'reserved' tags for >> precisely this purpose, namely non-I/O tags which live off a separate >> tag pool. That guarantees that these commands can always be sent, >> and won't be influenced by tag starvation from the I/O tag pool. >> This patchset enables the use of reserved tags for the SCSI midlayer >> by allocating a virtual LUN for the HBA itself which just serves >> as a resource to allocate valid tags from. >> This removes quite some hacks which were required for some >> drivers (eg. fnic or snic), and allows the use of tagset >> iterators within the drivers. >> > > Hey Hannes, > > I was trying to port some iscsi patches to this set. One question I had > is how to handle if my driver implements init_cmd_priv, and wants to use > the reserved cmds for a non scsi IO. My case I want to use them for cmds > like a iscsi nop/ping, device/target reset or login request. > > There is no bit to way to tell if at init_cmd_priv time the cmd will be > for a reserved or non reserved cmd right? If not, I was wondering should > I do: > > 1. in libiscsi, allocate an array of size $reserved_cmds with non_scsi_cmds > structs. When I need to do a non scsi cmd do blk_mq_get_tag on the host's > tags to get a reserved tag then use that to lookup a struct in my array? > > 2. in libiscsi when I need to do a non scsi cmd do a scsi_get_internal_cmd. > At this time allocate the non_scsi_cmd struct parts. > You sure you will need to allocate additional stuff? The request already comes with the request, scsi, and driver private bits (ie the additional space from .cmd_size) allocated. And yes, you can tell in init_cmd_priv() if the command is coming from the private pool; I had a helper 'req_is_reserved' once, I thought it's still there ... Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@xxxxxxx +49 911 74053 688 SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg HRB 36809 (AG Nürnberg), GF: Felix Imendörffer
