Re: RFC: mmap(PROT_READ, MAP_SHARED) fails if !writepage.

[Linus Torvalds]

On Fri, 8 Nov 2002, David Woodhouse wrote:
> 
> It's a read-only mapping. Whether it's shared or private is not relevant,
> surely, since those affect only the behaviour if we write to it -- which we 
> can't. 

But why do you expect to be able to mmap shared something you opened RW in
the first place, if the filesystem cannot handle writable m appings?

> I don't _really_ want a shared mapping; all I want is for the fsx-linux
> stress test to run, and find interesting breakage on my file system to keep
> me from getting bored (what are Friday nights for, after all?).

Ok, it's good to have tests, but it sounds like the test is broken.

> As shipped, fsx-linux uses PROT_READ, MAP_SHARED on its test file

Ad shipped, the kernel doesn't allow that.

Notice the pattern here? "As shipped". You have two choices: make 
gratuitous changes to the kernel to make some random test happy, or fix 
the test.

I think you should fix the test. The kernel change buys you _zero_ new 
features.

		Linus