On Fri, Aug 18, 2017 at 09:43:19AM +0200, Hannes Reinecke wrote: > On 08/18/2017 09:38 AM, Omar Sandoval wrote: > > On Fri, Aug 18, 2017 at 09:18:52AM +0200, Hannes Reinecke wrote: > >> On 08/18/2017 08:15 AM, Omar Sandoval wrote: > >>> From: Omar Sandoval <osandov@xxxxxx> > >>> > >>> When I was writing a test for the new loop device block size > >>> functionality, I realized that the interface is kind of dumb: > >>> > >>> - lo_init[0] is never filled in with the logical block size we > >>> previously set > >>> - lo_flags returned from LOOP_GET_STATUS will have LO_FLAGS_BLOCKSIZE > >>> set if we previously called LOOP_SET_STATUS with LO_FLAGS_BLOCKSIZE > >>> set, which doesn't really mean anything > >>> > >>> Instead, for LOOP_GET_STATUS, let's always fill in lo_init[0] and set > >>> the LO_FLAGS_BLOCKSIZE flag to indicate we support it. > >>> > >>> Signed-off-by: Omar Sandoval <osandov@xxxxxx> > >>> --- > >>> drivers/block/loop.c | 33 +++++++++++++++++---------------- > >>> 1 file changed, 17 insertions(+), 16 deletions(-) > >>> > >> Phew. 'Dumb interface'. > >> 'tis wasn't me who designed the interface; > >> Backwards compability are the watchwords here. > >> Personally, I would have loved to design a new interface. > >> > >> I've got quite some flak for daring to break existing interfaces, most > >> notably setting logical and physical blocksize per default (which I > >> would _love_ to have done, seeing that it really makes sense here). > >> But as this would change the behaviour I've gone through pains (and > >> several _years_ of iterations) to get this sorted. > >> > >> So if you design a blocktest for that ensure that > >> a) the sysfs attributes before and after the patch are _identical_ > >> b) the sysfs attributes will only change if the 'LO_FLAGS_BLOCKSIZE' > >> flag has been set > >> and > >> c) validate the written blocksizes; this is required to be able to > >> install bootloaders there > >> > >> This whole interface was designed such that you can prepare bootable > >> diskimages for S/390 DASDs, which use a native 4k blocksize. > > > > Hi, Hannes, > > > > Wasn't insulting you at all, the only part of the interface I'm > > complaining about is LOOP_GET_STATUS missing information :) > > > Sure. Just saying. > But please make sure only to return that information if the > LO_FLAGS_BLOCKSIZE flag is set; otherwise there's a rick of confusing > losetup. I actually checked losetup, it works just fine with LO_FLAGS_BLOCKSIZE always set and lo_init[0] always filled in.
