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[RFC][PATCH 0/6] Enhanced file stat system call

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  [RFC][PATCH 0/6] Enhanced file stat system call David Howells <dhowells@redhat.com> - 2016-04-29 15:00 +0200
    [PATCH 4/6] statx: NFS: Return enhanced file attributes David Howells <dhowells@redhat.com> - 2016-04-29 15:00 +0200
      Re: [PATCH 4/6] statx: NFS: Return enhanced file attributes Andreas Dilger <adilger@dilger.ca> - 2016-05-03 00:50 +0200
    [PATCH 6/6] statx: CIFS: Return enhanced attributes David Howells <dhowells@redhat.com> - 2016-04-29 15:00 +0200
    [PATCH 3/6] statx: Ext4: Return enhanced file attributes David Howells <dhowells@redhat.com> - 2016-04-29 15:00 +0200
      Re: [PATCH 3/6] statx: Ext4: Return enhanced file attributes Andreas Dilger <adilger@dilger.ca> - 2016-05-03 00:50 +0200
        Re: [PATCH 3/6] statx: Ext4: Return enhanced file attributes David Howells <dhowells@redhat.com> - 2016-05-03 22:30 +0200
      Re: [PATCH 3/6] statx: Ext4: Return enhanced file attributes Christoph Hellwig <hch@infradead.org> - 2016-05-08 10:40 +0200
    [PATCH 5/6] statx: Make windows attributes available for CIFS,  NTFS and FAT to use David Howells <dhowells@redhat.com> - 2016-04-29 15:10 +0200
      Re: [PATCH 5/6] statx: Make windows attributes available for CIFS, NTFS and FAT to use Andreas Dilger <adilger@dilger.ca> - 2016-05-03 01:00 +0200
        Re: [PATCH 5/6] statx: Make windows attributes available for CIFS, NTFS and FAT to use David Howells <dhowells@redhat.com> - 2016-05-03 22:30 +0200
      Re: [PATCH 5/6] statx: Make windows attributes available for CIFS,  NTFS and FAT to use Christoph Hellwig <hch@infradead.org> - 2016-05-08 10:40 +0200
    [PATCH 2/6] statx: AFS: Return enhanced file attributes David Howells <dhowells@redhat.com> - 2016-04-29 15:20 +0200
    Re: [RFC][PATCH 0/6] Enhanced file stat system call Jeff Layton <jlayton@poochiereds.net> - 2016-04-30 23:10 +0200
    Re: [PATCH 1/6] statx: Add a system call to make enhanced file info available David Howells <dhowells@redhat.com> - 2016-05-03 18:00 +0200
    Re: [RFC][PATCH 0/6] Enhanced file stat system call Arnd Bergmann <arnd@arndb.de> - 2016-05-04 15:50 +0200
      Re: [RFC][PATCH 0/6] Enhanced file stat system call Steve French <smfrench@gmail.com> - 2016-05-06 04:10 +0200
        Re: [RFC][PATCH 0/6] Enhanced file stat system call Arnd Bergmann <arnd@arndb.de> - 2016-05-09 15:10 +0200
    Re: [PATCH 1/6] statx: Add a system call to make enhanced file info  available Dave Chinner <david@fromorbit.com> - 2016-05-05 01:00 +0200
      Re: [PATCH 1/6] statx: Add a system call to make enhanced file info available NeilBrown <nfbrown@novell.com> - 2016-05-05 02:20 +0200
        Re: [PATCH 1/6] statx: Add a system call to make enhanced file info  available Jeff Layton <jlayton@poochiereds.net> - 2016-05-05 21:50 +0200
          Re: [PATCH 1/6] statx: Add a system call to make enhanced file info available David Howells <dhowells@redhat.com> - 2016-05-05 22:10 +0200
            Re: [PATCH 1/6] statx: Add a system call to make enhanced file info  available Dave Chinner <david@fromorbit.com> - 2016-05-06 03:50 +0200
          Re: [PATCH 1/6] statx: Add a system call to make enhanced file info  available bfields@fieldses.org (J. Bruce Fields) - 2016-05-06 20:10 +0200
      Re: [PATCH 1/6] statx: Add a system call to make enhanced file info  available bfields@fieldses.org (J. Bruce Fields) - 2016-05-06 20:30 +0200
        Re: [PATCH 1/6] statx: Add a system call to make enhanced file info  available Dave Chinner <david@fromorbit.com> - 2016-05-09 03:50 +0200
          Re: [PATCH 1/6] statx: Add a system call to make enhanced file info  available "J. Bruce Fields" <bfields@fieldses.org> - 2016-05-09 04:50 +0200
    Re: [PATCH 1/6] statx: Add a system call to make enhanced file info available NeilBrown <nfbrown@novell.com> - 2016-05-05 02:00 +0200
    Re: [PATCH 1/6] statx: Add a system call to make enhanced file info  available Christoph Hellwig <hch@infradead.org> - 2016-05-08 10:40 +0200
      Re: [PATCH 1/6] statx: Add a system call to make enhanced file info  available Jeff Layton <jlayton@poochiereds.net> - 2016-05-09 14:10 +0200
        Re: [PATCH 1/6] statx: Add a system call to make enhanced file info  available Christoph Hellwig <hch@infradead.org> - 2016-05-10 09:10 +0200
          Re: [PATCH 1/6] statx: Add a system call to make enhanced file info  available Jeff Layton <jlayton@poochiereds.net> - 2016-05-10 15:30 +0200
      Re: [PATCH 1/6] statx: Add a system call to make enhanced file info available David Howells <dhowells@redhat.com> - 2016-05-09 15:00 +0200
        Re: [PATCH 1/6] statx: Add a system call to make enhanced file info available David Howells <dhowells@redhat.com> - 2016-05-09 15:10 +0200
        Re: [PATCH 1/6] statx: Add a system call to make enhanced file info  available Trond Myklebust <trondmy@primarydata.com> - 2016-05-09 15:40 +0200
        Re: [PATCH 1/6] statx: Add a system call to make enhanced file info  available Christoph Hellwig <hch@infradead.org> - 2016-05-10 09:10 +0200
          Re: [PATCH 1/6] statx: Add a system call to make enhanced file info available David Howells <dhowells@redhat.com> - 2016-05-10 10:30 +0200
            Re: [PATCH 1/6] statx: Add a system call to make enhanced file info  available Christoph Hellwig <hch@infradead.org> - 2016-05-12 11:20 +0200
      Re: [PATCH 1/6] statx: Add a system call to make enhanced file info available David Howells <dhowells@redhat.com> - 2016-05-09 15:40 +0200
        Re: [PATCH 1/6] statx: Add a system call to make enhanced file info  available Christoph Hellwig <hch@infradead.org> - 2016-05-10 09:10 +0200
          Re: [PATCH 1/6] statx: Add a system call to make enhanced file info available David Howells <dhowells@redhat.com> - 2016-05-10 10:50 +0200
            Re: [PATCH 1/6] statx: Add a system call to make enhanced file info  available Christoph Hellwig <hch@infradead.org> - 2016-05-12 11:20 +0200
      Re: [PATCH 1/6] statx: Add a system call to make enhanced file info available David Howells <dhowells@redhat.com> - 2016-05-09 15:50 +0200

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#1397854 — Re: [PATCH 1/6] statx: Add a system call to make enhanced file info available

Christoph Hellwig <hch@infradead.org> wrote:

> All of these are easily available.  But why special case them so that
> userspace must not ask for them?  This makes an otherwise totally
> regular interface special now.  Note that filesystems could always fill
> it out anyway and set it in the return mask.

Because it would be a waste of bits in the mask.  Is there a point in having
bits that are always going to be set unconditionally when we can just
*document* that these few fields are always going to be set.

I'm sure people can cope with the concept that some data are provided
unconditionally and don't have bits and the rest are provided conditionally
and do have bits.

I admit, though, that i_mode is tricky, since it's actually the combination of
two pieces of information - one conditional (permission bits) and one normally
unconditional (file type).  Possibly then i_mode should have two flags since I
can think of situations where the file type might be other - reparse points,
automount points.

So yes, you can look on it as there are special cases.  However, if I can drop
stat emulation support, everything resolves down to the following classes:

 (1) Stuff that's unconditional: st_dev, st_blksize, st_information (maybe).

 (2) st_mode & S_IFMT.  Unconditional or conditional?  I'm not sure.

 (3) Stuff that's conditional: st_mode & ~S_IFMT, st_rdev, st_ino, ...
     Basically everything else.

David

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#1399819 — Re: [PATCH 1/6] statx: Add a system call to make enhanced file info available

On Tue, May 10, 2016 at 09:43:43AM +0100, David Howells wrote:
> Christoph Hellwig <hch@infradead.org> wrote:
> 
> > All of these are easily available.  But why special case them so that
> > userspace must not ask for them?  This makes an otherwise totally
> > regular interface special now.  Note that filesystems could always fill
> > it out anyway and set it in the return mask.
> 
> Because it would be a waste of bits in the mask.  Is there a point in having
> bits that are always going to be set unconditionally when we can just
> *document* that these few fields are always going to be set.

And what exaxtly is the cost of these bits?

> So yes, you can look on it as there are special cases.  However, if I can drop
> stat emulation support, everything resolves down to the following classes:
> 
>  (1) Stuff that's unconditional: st_dev, st_blksize, st_information (maybe).
> 
>  (2) st_mode & S_IFMT.  Unconditional or conditional?  I'm not sure.
> 
>  (3) Stuff that's conditional: st_mode & ~S_IFMT, st_rdev, st_ino, ...
>      Basically everything else.

If we at least go down to one set of conditional and one optional that's
at least much better than what we currently have.

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#1397070 — Re: [PATCH 1/6] statx: Add a system call to make enhanced file info available

Christoph Hellwig <hch@infradead.org> wrote:

> And please prepare a man page to document this system call properly.

I intend to - but when it's stabilised sufficiently to warrant inclusion.

David

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