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Subjectvm: weird behaviour when munmapping
Hmm, I'm probably missing something but I don't see what. Please be
nice even if the question is really stupid ;)

I'm looking at mmap.c code and to understand it I decided to implement
a dumb char device that implement its own foo_mmap() method. In this
method it defined its own vma ops:

static void foo_vma_open(struct vm_area_struct *vma)
static void foo_vma_close(struct vm_area_struct *vma)

A dumb application mmap the device in order to make foo_mmap() install
the vma ops.

mmap(NULL, 16384, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);

mmap returned 0x2aaae000 for example. Until now, foo_vma_open() and
foo_vma_close() are not called.

Now I want to unmap the first part of the previous mapping to see how
vma ops are called. So I did:

munmap(0x2aaae000, 1024);

and here's what happen:

foo_vma_open(vma) is called with:
vma->vm_start = 0x2aaae000
vma->vm_end = 0x2aaaf000

foo_vma_close(vma) is called with:
vma->vm_start = 0x2aaae000
vma->vm_end = 0x2aaaf000

However I would have expected:

foo_vma_open(vma) is called with:
vma->vm_start = 0x2aaaf000
vma->vm_end = 0x2aaab2000

foo_vma_close(vma) is called with:
vma->vm_start = 0x2aaae000
vma->vm_end = 0x2aaaf000

Can anybody tell me why I get this behaviour ?

thanks

Francis








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