linux-kernel - Re: [PATCH 15/28] ovl: Open file with data except for the case of fsync

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Date:   Wed, 30 May 2018 11:48:26 -0400
From:   Vivek Goyal <vgoyal@...hat.com>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     Miklos Szeredi <mszeredi@...hat.com>,
        overlayfs <linux-unionfs@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 15/28] ovl: Open file with data except for the case of
 fsync

On Wed, May 30, 2018 at 05:12:16PM +0200, Miklos Szeredi wrote:
> >> From: Vivek Goyal <vgoyal@...hat.com>
> >>
> >> ovl_open() should open file which contains data and not open metacopy
> >> inode.  With the introduction of metacopy inodes, with current
> >> implementaion we will end up opening metacopy inode as well.
> >>
> >> But there can be certain circumstances like ovl_fsync() where we want to
> >> allow opening a metacopy inode instead.
> >>
> >> Hence, change ovl_open_realfile() and add _ovl_open_real() and add extra
> >> parameter which specifies whether to allow opening metacopy inode or not.
> >> If this parameter is false, we look for data inode and open that.
> >>
> >> This should allow covering both the cases.
> >>
> >> Signed-off-by: Vivek Goyal <vgoyal@...hat.com>
> >> Reviewed-by: Amir Goldstein <amir73il@...il.com>
> >> Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
> >> ---
> >>  fs/overlayfs/file.c | 39 ++++++++++++++++++++++++++++++---------
> >>  1 file changed, 30 insertions(+), 9 deletions(-)
> >>
> >> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> >> index 266692ce9a9a..c7738ef492c8 100644
> >> --- a/fs/overlayfs/file.c
> >> +++ b/fs/overlayfs/file.c
> >> @@ -14,11 +14,20 @@
> >>  #include <linux/uio.h>
> >>  #include "overlayfs.h"
> >>
> >> -static struct file *ovl_open_realfile(const struct file *file)
> >> +static char ovl_whatisit(struct inode *inode, struct inode *realinode)
> >> +{
> >> +     if (realinode != ovl_inode_upper(inode))
> >> +             return 'l';
> >> +     if (ovl_has_upperdata(inode))
> >> +             return 'u';
> >> +     else
> >> +             return 'm';
> >> +}
> >> +
> >> +static struct file *ovl_open_realfile(const struct file *file,
> >> +                                   struct inode *realinode)
> >>  {
> >>       struct inode *inode = file_inode(file);
> >> -     struct inode *upperinode = ovl_inode_upper(inode);
> >> -     struct inode *realinode = upperinode ?: ovl_inode_lower(inode);
> >>       struct file *realfile;
> >>       const struct cred *old_cred;
> >>
> >> @@ -28,7 +37,7 @@ static struct file *ovl_open_realfile(const struct file *file)
> >>       revert_creds(old_cred);
> >>
> >>       pr_debug("open(%p[%pD2/%c], 0%o) -> (%p, 0%o)\n",
> >> -              file, file, upperinode ? 'u' : 'l', file->f_flags,
> >> +              file, file, ovl_whatisit(inode, realinode), file->f_flags,
> >>                realfile, IS_ERR(realfile) ? 0 : realfile->f_flags);
> >>
> >>       return realfile;
> >> @@ -72,17 +81,24 @@ static int ovl_change_flags(struct file *file, unsigned int flags)
> >>       return 0;
> >>  }
> >>
> >> -static int ovl_real_fdget(const struct file *file, struct fd *real)
> >> +static int ovl_real_fdget_meta(const struct file *file, struct fd *real,
> >> +                            bool allow_meta)
> >>  {
> >>       struct inode *inode = file_inode(file);
> >> +     struct inode *realinode;
> >>
> >>       real->flags = 0;
> >>       real->file = file->private_data;
> >>
> >> +     if (allow_meta)
> >> +             realinode = ovl_inode_real(inode);
> >> +     else
> >> +             realinode = ovl_inode_realdata(inode);
> >> +
> >>       /* Has it been copied up since we'd opened it? */
> >> -     if (unlikely(file_inode(real->file) != ovl_inode_real(inode))) {
> >> +     if (unlikely(file_inode(real->file) != realinode)) {
> >>               real->flags = FDPUT_FPUT;
> >> -             real->file = ovl_open_realfile(file);
> >> +             real->file = ovl_open_realfile(file, realinode);
> >>
> >>               return PTR_ERR_OR_ZERO(real->file);
> >>       }
> >> @@ -94,6 +110,11 @@ static int ovl_real_fdget(const struct file *file, struct fd *real)
> >>       return 0;
> >>  }
> >>
> >> +static int ovl_real_fdget(const struct file *file, struct fd *real)
> >> +{
> >> +     return ovl_real_fdget_meta(file, real, false);
> >> +}
> >> +
> >>  static int ovl_open(struct inode *inode, struct file *file)
> >>  {
> >>       struct dentry *dentry = file_dentry(file);
> >> @@ -107,7 +128,7 @@ static int ovl_open(struct inode *inode, struct file *file)
> >>       /* No longer need these flags, so don't pass them on to underlying fs */
> >>       file->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);
> >>
> >> -     realfile = ovl_open_realfile(file);
> >> +     realfile = ovl_open_realfile(file, ovl_inode_real(file_inode(file)));
> 
> That was meant to be
> 
> +     realfile = ovl_open_realfile(file, ovl_inode_realdata(file_inode(file)));
> 
> Is that correct?

Yes, that's correct.

While we are at it, can we also update patch changelog. I see that
_ovl_open_real() is not there anymore.

Thanks
Vivek