On Wed, Jan 29, 2014 at 1:20 AM, H. Peter Anvin <hpa@xxxxxxxxx> wrote: > On 01/28/2014 04:14 PM, Kay Sievers wrote: >>> >>> If the "single owner" is determined by the file structure (e.g. via a >>> fcntl as opposed to a ioctl), then presumably we would simply deny an >>> attempt to open the inode and create a new file structure for it. >>> >>> On Linux, /proc/$PID/fd is an open as opposed to a dup (as much as I >>> personally don't like those semantics, they are well set in stone at >>> this point) so it satisfies your requirements. >> >> If that all could be made working, for the kdbus case we would be fine >> with requiring *any* tmpfs mount, create a new memfd from there with >> O_TMPFILE, and use new fcntl() definitios to protect/seal/unseal and >> identify that fd. >> >> For the more restricted cases like Android that tmpfs mount could get >> a mount option to not allow the creation of any non-unlinked file, I >> guess. >> > > Right, that would be the idea. I like your idea. Sounds worth trying, if you think we can make the protection/sealing work without too much ugly workarounds. With the filesystem as a "domain" / the root for all the unlinked shmem files, we could even mount a separate tmpfs for every logged-in user, and put the quota on the user that way. It will still not solve the /dev/shm/ or /tmp quota problem, but it would at least not get bigger with every new shmem user we invent. :) Kay -- 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>