When will you use mmap map_fixed

Question

I look at different flags for the mmap function, namely MAP_FIXED, MAP_SHARED, MAP_PRIVATE. Can someone explain the purpose of MAP_FIXED to me? There is no guarantee that the address space will be used in the first place.

Answer 1

MAP_FIXEDis dup2for memory mappings and is useful in the same situations when it dup2is useful for file descriptors: when you want to perform a replacement operation that atomically reassigns a resource identifier (memory range in case MAP_FIXED, or fd in case dup2) to refer to a new resource without race capability, where it can be reassigned to something else if you first released an old resource and then tried to return it to a new resource.

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Answer 2

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