Messages in this thread | | | Date | Tue, 22 Feb 2000 18:46:02 +0100 (MET) | From | Richard Guenther <> | Subject | mmap/munmap semantics |
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Hi!
With the ongoing development of GLAME there arise the following problems with the backing-store management, which is a mmaped file and does "userspace virtual memory management": - I cannot see a way to mmap a part of the file but set the contents initially to zero, i.e. I want to setup an initially dirty zero-mapping which is assigned to a part of the file. Currently I'm just mmaping the part and do the zeroing by reading from /dev/zero (which does as I understand from the kernel code just create this zero mappings) - is there a more portable way to achieve this? - I need to "drop" a mapping sometimes without writing the contents back to disk - I cannot see a way to do this with linux currently. Ideally a hole could be created in the mmapped file on drop time - is this possible at all with the VFS/ext2 at the moment (creating a hole in a file by dropping parts of it)?
So for the first case we could add a flag to mmap like MAP_ZERO to indicate a zero-map (dirty).
For the second case either the munmap call needs to be extended or some sort of madvise with a MADV_CLEAN flag? Or we can just adjust mprotect(PROT_NONE) and subsequent munmap() to do the dropping?
Richard.
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