Re: [RFC] correct flags to f_mode conversion in __dentry_open
- From: James Morris <jmorris@xxxxxxxxx>
- Date: Thu, 22 May 2008 12:10:33 +1000 (EST)
On Wed, 21 May 2008, Michael Kerrisk wrote:
Christoph Hellwig wrote:
On Sat, Mar 15, 2008 at 05:59:52PM -0400, Alan Cox wrote:
does 11 really mean and should it really always be mapped to (FMODE_READWe've always mapped 3 to "no permission" to read or write. It's a linuxism
| FMODE_WRITE) or should it continue to get mapped to 'no permission?'
I've tripped over this recently aswell. It would for sure be useful
to add a sumbolic O_FOO constant for this magic value '3' and document
it in the manpage.
Late follow-up to this thread
(http://thread.gmane.org/gmane.linux.kernel/653123):
I propose to add the following text to the open(2) man page.
Unlike the other values that can be specified in flags,
the access mode values O_RDONLY, O_WRONLY, and O_RDWR, do
not specify individual bits. Rather, they define the low
order two bits of flags, and are defined respectively as
0, 1, and 2. In other words, the combination O_RDONLY |
O_WRONLY is a logical error, and certainly does not have
the same meaning as O_RDWR. Linux reserves the special,
non-standard access mode 3 (binary 11) in flags to mean:
check for read and write permission on the file and
return a descriptor that can't be used for reading or
writing. This non-standard access mode is used by some
Linux drivers to return a descriptor that is only to be
used for device-specific ioctl(2) operations.
Seem okay?
Looks good to me. We definitely need this documented.
- James
--
James Morris
<jmorris@xxxxxxxxx>
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- From: Michael Kerrisk
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