Changing vma's vm_file

[Robert Obryk]

Hello everyone,

Can a file_ops mmap routine change the vm_file in the vma? I assume
the file_ops of the substituted file won't break -- question is
whether anything else can.

The only thing during mmap syscall I can notice to depend on the value
of vm_file prior to call to f_op->mmap is the whole VM_DENYWRITE
stuff. It confuses me somewhat, while it appears to do something,
while manual for mmap states that MAP_DENYWRITE is ignored. What does
it do now?

The problem I am trying to solve is creating a file which will, upon
being mmaped, duplicate a mapping belonging to a different process. I
plan to do this by substituting vm_file and calling proper f_op->mmap
in my file's f_op->mmap.

Thanks in advance for any advice,
Robert Obryk
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