Doubt on mmap file backend

[Prem Kumar]

We are trying to map the file and content is written in to specific offset.
In meanwhile, if try to access the mmap'd content at specified offset, we
are getting NULL value. we have not called msync() yet. the mmap called
with MAP_SHARED.
Is it possible that mmap content can differ on read after write or is this
the problem happening because read is called before the msync().Sorry ,it
is very generic question ..Wanted to know if any idea on the behavior.

Thanks,
Prem

[Poul-Henning Kamp]

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Post by Prem Kumar
Is it possible that mmap content can differ on read after write or is this
the problem happening because read is called before the msync().Sorry ,it
is very generic question ..Wanted to know if any idea on the behavior.

If you mean "read by another process", then yes. Only kernels with
integrated VM/buffers provide consistency without msync.