Re: [RFC PATCH 1/3] fs: define new read_iter rwf flag

[Matthew Wilcox <willy@infradead.org>]

On Thu, Sep 28, 2017 at 08:39:31AM -0400, Mimi Zohar wrote:
> Writing extended attributes requires exclusively taking the i_rwsem
> lock.  To synchronize the file hash calculation and writing the file
> hash as security.ima xattr, IMA-appraisal takes the i_rwsem lock
> exclusively before calculating the file hash.  (Once the file hash
> is calculated, the result is cached.  Taking the lock exclusively
> prevents calculating the file hash multiple times.)
> 
> Some filesystems have recently replaced their filesystem dependent
> lock with the global i_rwsem to read a file.  As a result, when IMA
> attempts to calculate the file hash, reading the file attempts to
> take the i_rwsem again.
> 
> To resolve this problem, this patch defines a new read_iter flag
> named "rwf" to indicate that the i_rwsem has already been taken
> exclusively.  Subsequent patches will set or test the "rwf" flag.

I don't like adding a bool parameter everywhere.  Why not add a flag
to the kiocb ki_flags?

#define IOCB_RWSEM_HELD		(1 << 8)