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Diffstat (limited to 'Documentation/nommu-mmap.txt')
| -rw-r--r-- | Documentation/nommu-mmap.txt | 46 |
1 files changed, 46 insertions, 0 deletions
diff --git a/Documentation/nommu-mmap.txt b/Documentation/nommu-mmap.txt index b88ebe4d808..7714f57caad 100644 --- a/Documentation/nommu-mmap.txt +++ b/Documentation/nommu-mmap.txt @@ -116,6 +116,9 @@ FURTHER NOTES ON NO-MMU MMAP (*) A list of all the mappings on the system is visible through /proc/maps in no-MMU mode. + (*) A list of all the mappings in use by a process is visible through + /proc/<pid>/maps in no-MMU mode. + (*) Supplying MAP_FIXED or a requesting a particular mapping address will result in an error. @@ -125,6 +128,49 @@ FURTHER NOTES ON NO-MMU MMAP error will result if they don't. This is most likely to be encountered with character device files, pipes, fifos and sockets. + +========================== +INTERPROCESS SHARED MEMORY +========================== + +Both SYSV IPC SHM shared memory and POSIX shared memory is supported in NOMMU +mode. The former through the usual mechanism, the latter through files created +on ramfs or tmpfs mounts. + + +======= +FUTEXES +======= + +Futexes are supported in NOMMU mode if the arch supports them. An error will +be given if an address passed to the futex system call lies outside the +mappings made by a process or if the mapping in which the address lies does not +support futexes (such as an I/O chardev mapping). + + +============= +NO-MMU MREMAP +============= + +The mremap() function is partially supported. It may change the size of a +mapping, and may move it[*] if MREMAP_MAYMOVE is specified and if the new size +of the mapping exceeds the size of the slab object currently occupied by the +memory to which the mapping refers, or if a smaller slab object could be used. + +MREMAP_FIXED is not supported, though it is ignored if there's no change of +address and the object does not need to be moved. + +Shared mappings may not be moved. Shareable mappings may not be moved either, +even if they are not currently shared. + +The mremap() function must be given an exact match for base address and size of +a previously mapped object. It may not be used to create holes in existing +mappings, move parts of existing mappings or resize parts of mappings. It must +act on a complete mapping. + +[*] Not currently supported. + + ============================================ PROVIDING SHAREABLE CHARACTER DEVICE SUPPORT ============================================ |