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    <p>This fragment:</p> <blockquote> <p>A consequence of this design is that a virtual page that maps a file privately sees changes done to the file by other programs <em>as long as the page has only been read from</em>.</p> </blockquote> <p>is telling you that the kernel cheats a little bit in the name of optimization. Even though you've asked for a private mapping, the kernel will actually give you a shared one at first. Then, if you write the page, it becomes private.</p> <p>Observe that this "cheating" doesn't matter (doesn't make any difference) if all processes which are accessing the file are doing it with <code>MAP_PRIVATE</code>, because no actual changes to the file will ever occur in that case. Different processes' mappings will simply be upgraded from "fake cheating MAP_PRIVATE" to true "MAP_PRIVATE" at different times according to whenever each process first writes to the file. This is probably a common scenario. It's only if the file is being concurrently updated by other means (<code>MAP_SHARED</code> with <code>PROT_WRITE</code> or else regular, non-<code>mmap</code> I/O operations) that it makes a difference.</p> <blockquote> <p>I'm told that pages itself can also have permissions (read/write/execute).</p> </blockquote> <p>Sure, they can. You have to ask for the permissions you want when you initially map the file, in fact: the third argument to <code>mmap</code>, which will be a combination of <code>PROT_READ</code>, <code>PROT_WRITE</code>, <code>PROT_EXEC</code>, and <code>PROT_NONE</code>.</p>
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    1. COThank you! Got it.
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Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

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