On Tue, Jun 17, 2014 at 9:36 AM, David Herrmann <dh.herrmann@xxxxxxxxx> wrote: > Hi > > On Tue, Jun 17, 2014 at 6:20 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: >> Can you summarize why holes can't be reliably backed by the zero page? > > To answer this, I will quote Hugh from "PATCH v2 1/3": > >> We do already use the ZERO_PAGE instead of allocating when it's a >> simple read; and on the face of it, we could extend that to mmap >> once the file is sealed. But I am rather afraid to do so - for >> many years there was an mmap /dev/zero case which did that, but >> it was an easily forgotten case which caught us out at least >> once, so I'm reluctant to reintroduce it now for sealing. >> >> Anyway, I don't expect you to resolve the issue of sealed holes: >> that's very much my territory, to give you support on. > > Holes can be avoided with a simple fallocate(). I don't understand why > I should make SEAL_WRITE do the fallocate for the caller. During the > discussion of memfd_create() I was told to drop the "size" parameter, > because it is redundant. I don't see how this implicit fallocate() > does not fall into the same category? > I'm really confused now. If I SEAL_WRITE a file, and then I mmap it PROT_READ, and then I read it, is that a "simple read"? If so, doesn't that mean that there's no problem? --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
