Hi On Tue, Jun 17, 2014 at 2:13 PM, Florian Weimer <fweimer@xxxxxxxxxx> wrote: > On 06/17/2014 12:10 PM, David Herrmann wrote: > >>>> The file might have holes, therefore, you'd have to allocate backing >>>> pages. This might hit a soft-limit and fail. To avoid this, use >>>> fallocate() to allocate pages prior to mmap() >>> >>> >>> This does not work because the consuming side does not know how the >>> descriptor was set up if sealing does not imply that. >> >> >> The consuming side has to very seals via F_GET_SEALS. After that, it >> shall do a simple fallocate() on the whole file if it wants to go sure >> that all pages are allocated. Why shouldn't that be possible? Please >> elaborate. > > > Hmm. You permit general fallocate even for WRITE seals. That's really > unexpected. SEAL_WRITE prevents modifications of file-content. fallocate() does not modify file-contents, so I think it's not unexpected that fallocate() is still allowed. > The inode_newsize_ok check in shmem_fallocate can result in SIGXFSZ, which > doesn't seem to be what's intended here. It can only result in SIGXFSZ if you _increase_ the file-size with fallocate(). You shouldn't do that if you only verify that holes are allocated. Hence, a simple fallocate(st.st_size) cannot result in SIGXFSZ. Obviously, this requires SEAL_SHRINK to prevent the remote site to shrink the file while you call fallocate(). But SEAL_WRITE usually goes together with SEAL_SHRINK for obvious reasons. > Will the new pages attributed to the process calling fallocate, or to the > process calling memfd_create? Pages are always allocated by the caller and charged on current->mm (current process). Thanks David -- 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>