was just asked to take a look at how SATA II port multipliers are supported in the linux kernel and, in the midst of all the code and header files, what seems to be missing is a simple graphic of the main structures and how many of them there are. let me elucidate. imagine, say, a 1-to-4 PMP -- single port multiplexing to four SATA HDDs. from include/linux/libata.h, i can see the ATA-related structures that will be involved, but it would be just ducky if there was a short description as to *how* *many* of each would be involved in this scenario; that is, a simple counting demonstration would be massively informative. first, it appears that there would be a single ata_port structure: struct ata_port { struct Scsi_Host *scsi_host; /* our co-allocated scsi host */ struct ata_port_operations *ops; spinlock_t *lock; /* Flags owned by the EH context. Only EH should touch these once the port is active */ unsigned long flags; /* ATA_FLAG_xxx */ ... snip ... where one of the possible "flags" settings is: ATA_FLAG_PMP = (1 << 19), /* controller supports PMP */ so, having only glanced at all of this so far, i assume i would have one "struct ata_port" with that flag set. on the other hand, it would appear i would have four "struct ata_link"s: struct ata_link { struct ata_port *ap; int pmp; /* port multiplier port # */ ... snip ... finally, what about "struct ata_device": struct ata_device { struct ata_link *link; unsigned int devno; /* 0 or 1 */ ... snip ... not having read any further just yet, it's not clear whether there would be one or four of those, depending on how libata views the storage devices themselves, but i'm sure i'll figure it out as i keep reading. in the end, it would be terrifically useful if there was a simple example of how all these structures connected to support a basic scenario. is that written down anywhere? it doesn't need to be crazy comprehensive, just the enumeration of the structures involved. thoughts? rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================