99a4a90c8e
We fall back to lookup+create (instead of atomic_open) in several cases: 1) we don't have write access to filesystem and O_TRUNC is present in the flags. It's not something we want ->atomic_open() to see - it just might go ahead and truncate the file. However, we can pass it the flags sans O_TRUNC - eventually do_open() will call handle_truncate() anyway. 2) we have O_CREAT | O_EXCL and we can't write to parent. That's going to be an error, of course, but we want to know _which_ error should that be - might be EEXIST (if file exists), might be EACCES or EROFS. Simply stripping O_CREAT (and checking if we see ENOENT) would suffice, if not for O_EXCL. However, we used to have ->atomic_open() fully responsible for rejecting O_CREAT | O_EXCL on existing file and just stripping O_CREAT would've disarmed those checks. With nothing downstream to catch the problem - FMODE_OPENED used to be "don't bother with EEXIST checks, ->atomic_open() has done those". Now EEXIST checks downstream are skipped only if FMODE_CREATED is set - FMODE_OPENED alone is not enough. That has eliminated the need to fall back onto lookup+create path in this case. 3) O_WRONLY or O_RDWR when we have no write access to filesystem, with nothing else objectionable. Fallback is (and had always been) pointless. IOW, we don't really need that fallback; all we need in such cases is to trim O_TRUNC and O_CREAT properly. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.