On Sun, Mar 23, 2014 at 03:02:44PM +0100, Jan Kara wrote: > On Sat 22-03-14 02:43:20, Darrick J. Wong wrote: > > On Fri, Mar 21, 2014 at 07:32:16PM -0700, Darrick J. Wong wrote: > > > On Fri, Mar 21, 2014 at 05:29:09PM -0700, Zach Brown wrote: > > > > I'll admit, though, that I don't really like having to fetch the 'has' > > > > bits first to find out how large the rest of the struct is. Maybe > > > > that's not worth worrying about. > > > > > > I'm not worrying about having to pluck 'has' out of the structure, but needing > > > a function to tell me how big of a buffer I need for a given pile of flags > > > seems ... icky. But maybe the ease of modifying strace and security auditors > > > would make it worth it? > > > > How about explicitly specifying the structure size in struct some_more_args, > > and checking that against whatever we find in .has? Hm. I still think that's > > too clever for my brain to keep together for long. > > > > I'm also nervous that we could be creating this monster of a structure wherein > > some user wants to tack the first and last hints ever created onto an IO, so > > now we have to lug this huge structure around that has space for hints that > > we're not going to use, and most of which is zeroes. > Well, why does it matter that the structure would be big? Are do you > think the memory consumption would matter? I doubt the memory consumption will be a big deal (compared to the size of the IOs), but I'm a little concerned about the overhead of copying a mostly-zeroes user buffer into the kernel. I guess it's not a big deal to copy the whole thing now and if people complain about the overhead, switch it to let the IO attribute controllers selectively copy_from_user later. --D > > Honza > -- > Jan Kara <jack@xxxxxxx> > SUSE Labs, CR > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>