Transcript Studying ‘mmap()/munmap()’ How we can use our ‘toolbox’ of effects of ‘mmap()/munmap()’

Studying ‘mmap()/munmap()’
How we can use our ‘toolbox’ of
kernel modules to examine the
effects of ‘mmap()/munmap()’
Experiment #1
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Remember our ‘vma.c’ module?
It creates a ‘/proc’ file
It shows a task’s virtual memory areas
NOTE: It works only for the ‘current’ task
We do BEFORE and AFTER comparisons
Details of our Plan #1
• Install the ‘vma.c’ module
• Install ‘mysis.c’ device-driver
• Write an application: ‘mmstudy1.cpp’
– Open the files ‘/dev/mysis’ and ‘/proc/vma’
– Read and display contents of ‘/proc/vma’
– Call ‘mmap()’ to map the video frame-buffer
– Read and display contents of ‘/proc/vma’
– Call ‘munmap()’ to unmap the frame-buffer
– Read and display contents of ‘/proc/vma’
Experiment #2
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We want to examine a task’s page-tables
We need to use our ‘ram.c’ device-driver
We also need a new ‘/proc’ file: ‘cr3.c’
CR3 = physical address of page-directory
Page-Directory = page-table addresses
We again do BEFORE and AFTER looks
Details of our Plan #2
• Install modules ‘cr3.c’ and ‘ram.c’
• Write an application: ‘mmstudy2.cpp’
– Open: /proc/cr3, ‘/dev/ram’ and ‘/dev/vram’
– Read page-directory and page-table(s)
– Call ‘mmap()’ to map the video frame-buffer
– Read page-directory and page-table(s)
– Call ‘munmap()’ to unmap the frame-buffer
– Read page-directory and page-table(s)
– Compare tables (to see if anything changed)
What to turn in today?
• Turn in a printout of your source-code:
– for ‘mmstudy1.cpp’ and for ‘mmstudy2.cpp’
• Turn in a printout of your program output:
– from ‘mmstudy1’ and from ‘mmstudy2’
• You may ask for assistance
– from Instructor, from TA, from classmembers