Messages in this thread | | | From | (Linus Torvalds) | Subject | Re: RFC: mmap(PROT_READ, MAP_SHARED) fails if !writepage. | Date | Fri, 8 Nov 2002 23:31:09 +0000 (UTC) |
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In article <24305.1036795742@passion.cambridge.redhat.com>, David Woodhouse <dwmw2@infradead.org> wrote: >Why does a _readonly_ mapping fail if the file system has no writepage >method? > >do_mmap_pgoff() sets VM_MAYWRITE on the vma and then generic_file_mmap() >refuses to allow it. > >Suggested patch below.... or should I just hack fsx-linux to use >MAP_PRIVATE for its readonly mappings and ignore it?
This is broken. Since it has VM_MAYWRITE, a subsequent mprotect() may mark it writable, and you you went boom.
If you really want a shared mapping, you'd better open with O_RDONLY, at which point the existing code should be perfectly happy and does the right thing.
In other words: the code is correct as-is.
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