On Wed, 2014-05-14 at 17:22 -0700, Andy Grover wrote: > On 05/14/2014 05:07 PM, Nicholas A. Bellinger wrote: > > On Wed, 2014-05-14 at 15:48 -0700, Andy Grover wrote: > >> Just like for pSCSI, if the transport sets get_write_cache, then it is > >> not valid to enable write cache emulation for it. Return an error. > >> > >> see https://bugzilla.redhat.com/show_bug.cgi?id=1082675 > >> > >> Reviewed-by: Chris Leech <cle...@redhat.com> > >> Signed-off-by: Andy Grover <agro...@redhat.com> > >> --- > >> drivers/target/target_core_device.c | 8 ++++---- > >> 1 file changed, 4 insertions(+), 4 deletions(-) > >> > >> diff --git a/drivers/target/target_core_device.c > >> b/drivers/target/target_core_device.c > >> index 65001e1..d461ecb 100644 > >> --- a/drivers/target/target_core_device.c > >> +++ b/drivers/target/target_core_device.c > >> @@ -798,10 +798,10 @@ int se_dev_set_emulate_write_cache(struct se_device > >> *dev, int flag) > >> pr_err("emulate_write_cache not supported for pSCSI\n"); > >> return -EINVAL; > >> } > >> - if (dev->transport->get_write_cache) { > >> - pr_warn("emulate_write_cache cannot be changed when underlying" > >> - " HW reports WriteCacheEnabled, ignoring request\n"); > >> - return 0; > >> + if (flag && > >> + dev->transport->get_write_cache) { > >> + pr_err("emulate_write_cache not supported for this device\n"); > >> + return -EINVAL; > >> } > >> > >> dev->dev_attrib.emulate_write_cache = flag; > > > > Allowing the target WCE bit to be disabled when the underlying device > > has WCE enabled is a recipe for disaster. > > > > How is the initiator supposed to know when to flush writes if the target > > is telling it that WCE is disabled. > > > > I'll take change to return -EINVAL here, but the other part is dangerous > > and wrong. > > This is for backstores like iblock, where we're actually getting WCE > yes/no from the backing block device. This configfs entry is not for WCE > yes/no, it is for WCE *emulation* yes/no. >
Huh..? The only thing that emulate_write_cache controls is the reporting of WCE via the caching mode page + EVPD=0x86 for FILEIO + RD backends. > So we should allow emulate_write_cache to be set to 0, because we're not > emulating the write cache value, we're using the actual value... but we > shouldn't allow it to be enabled if we're getting real WCE yes/no values. There is no point in touching the emulate_write_cache value for IBLOCK. It's already being ignored in spc_check_dev_wce() anyways. > So I'm still not seeing how this is not the right thing to do, > especially since it's identical to the pscsi case immediately above. PSCSI is providing it's own control bits, so the assignment in se_dev_set_emulate_write_cache() is pointless as well. Just get rid of the unnecessary flag check, and make both PSCSI + IBLOCK cases return -EINVAL. --nab -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
