Trond Myklebust wrote:
Yup, same problem. Why is this allowed? Does it really work correctly?
Assuming that the processes have _some_ method of synchronisation, then
I cannot see why it shouldn't be workable. Come to think of it, it might
even be possible to use O_DIRECT to provide that synchronisation (use
O_DIRECT to set a "lock" on the page, then modify it using mmap).
Whether or not there are people out there that actually _want_ to do
this is a different matter.
Mixing O_DIRECT i/o and cached i/o is probably a recipe for disaster,
unless the cooperating programs are very careful and very aware of how
the particular file system in the particular kernel implements direct
i/o and caching, including cache validation.
This seems like a dangerous enough area that denying mmap on a file which
has been opened with O_DIRECT by any process and denying open(O_DIRECT)
on a file which has been mmap'd would be a good thing. These things are
easy enough to keep track of, so it shouldn't be too hard to implement.
Thanx...
ps
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