I decided to do this by email instead of bugzilla so that it would be visible to everyone on the linux-scsi mailing list. Re: http://bugzilla.kernel.org/show_bug.cgi?id=7026 To recap: Joerg Schilling needs to be able to retrieve the max_sectors value for a SCSI device's request queue. Doing it via sysfs is rather clumsy, especially when only a file descriptor is available and not the device name. He has asked for an ioctl interface to provide the information. Is the patch below acceptable? Alan Stern Index: usb-2.6/block/scsi_ioctl.c =================================================================== --- usb-2.6.orig/block/scsi_ioctl.c +++ usb-2.6/block/scsi_ioctl.c @@ -97,6 +97,11 @@ static int sg_set_reserved_size(request_ return 0; } +static int sg_get_max_transfer_length(request_queue_t *q, int __user *p) +{ + return put_user(q->max_sectors << 9, p); +} + /* * will always return that we are ATAPI even for a real SCSI drive, I'm not * so sure this is worth doing anything about (why would you care??) @@ -558,6 +563,9 @@ int scsi_cmd_ioctl(struct file *file, st case SG_SET_RESERVED_SIZE: err = sg_set_reserved_size(q, arg); break; + case SG_GET_MAX_TRANSFER_LENGTH: + err = sg_get_max_transfer_length(q, arg); + break; case SG_EMULATED_HOST: err = sg_emulated_host(q, arg); break; Index: usb-2.6/drivers/scsi/sg.c =================================================================== --- usb-2.6.orig/drivers/scsi/sg.c +++ usb-2.6/drivers/scsi/sg.c @@ -927,6 +927,11 @@ sg_ioctl(struct inode *inode, struct fil case SG_GET_RESERVED_SIZE: val = (int) sfp->reserve.bufflen; return put_user(val, ip); + case SG_GET_MAX_TRANSFER_LENGTH: + if (sdp->detached || !sdp->device->request_queue) + return -ENODEV; + val = sdp->device->request_queue->max_sectors << 9; + return put_user(val, ip); case SG_SET_COMMAND_Q: result = get_user(val, ip); if (result) Index: usb-2.6/include/scsi/sg.h =================================================================== --- usb-2.6.orig/include/scsi/sg.h +++ usb-2.6/include/scsi/sg.h @@ -219,6 +219,8 @@ typedef struct sg_req_info { /* used by /* yields scsi midlevel's access_count for this SCSI device */ #define SG_GET_ACCESS_COUNT 0x2289 +/* Yields the SCSI device queue's max_sector value, in bytes */ +#define SG_GET_MAX_TRANSFER_LENGTH 0x228a #define SG_SCATTER_SZ (8 * 4096) /* Largest size (in bytes) a single scatter-gather list element can have. - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
