On Jun 28, 2008, at 7:33 PM, shailesh jain wrote: On Sat, Jun 28, 2008 at 7:09 PM, Michael Smith < email@hidden> wrote: On Jun 28, 2008, at 5:09 PM, shailesh jain wrote: 2) Also, I wanted to know about the option MAP_PRIVATE passed to the mmap call. When, this option
is passed, the modifications to the data are just made in-memory and are not reflected to the actual object. Now, If PROT_WRITE option is passed to the filesystem and the file is just opened for reading,
should the call fail ?
For mmap to succeed, the file should have been opened with the read flag always.
Not at all. A file can be written to without being read, whether the vector by which it is written is a mapped operation or a regular file write. Shouldn't it depend upon options {MAP_PRIVATE or MAP_SHARED } which are not passed to the filesystem ?
Also, I was looking at the mmap implementation but couldn't figure out how MAP_PRIVATE option was handled by kernel.
You're looking at the wrong place; you want to look at how the VM sets up the mapping against the object. You can expect to see the region marked copy-on-write, with an intermediate copy object involved.
These are supplied as a courtesy to the filesystem in case it wants/needs to make specific arrangements regarding the mapping.
Unless the filesystem is a proxy for a remote authority (e.g. a network filesystem), its responsibility regarding authorisation is limited to correctly answering questions posed by VNOP_GETATTR.
= Mike
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