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    SubjectRe: [PATCH 02/12] statx: Provide IOC flags for Windows fs attributes
    On Fri, Nov 20, 2015 at 02:54:47PM +0000, David Howells wrote:
    > Provide IOC flags for Windows fs attributes so that they can be retrieved (or
    > even altered) using the FS_IOC_[GS]ETFLAGS ioctl and read using statx().

    We have a real problem with numberspace used by FS_IOC_[GS]ETFLAGS.
    This ioctl was originally defined for use with ext2, but then later on
    other file systems decided they wanted to use the same ioctl for their
    file system, and so now we have the situation where some of the bits
    are used in a way where they are intended to be file system
    independent, and some are file system specific. And ext[234] use
    these bits as its on-disk encoding --- which given that
    FS_IOC[GS]ETFLAGS was originally ext[234] specific, is understandable,
    but it makes things really messy at this point.

    So for example, the bits you have chosen are in conflict with ext4's use:

    #define EXT4_INLINE_DATA_FL 0x10000000 /* Inode has inline data. */
    #define EXT4_PROJINHERIT_FL 0x20000000 /* Create with parents projid */

    > +#define FS_HIDDEN_FL 0x10000000 /* Windows hidden file attribute */
    > +#define FS_SYSTEM_FL 0x20000000 /* Windows system file attribute */
    > +#define FS_ARCHIVE_FL 0x40000000 /* Windows archive file attribute */


    As a result, I would suggest that we not try to use the
    FS_IOC_[GS]ETFLAGS number scheme for any new interface, so we're at
    least not making a bad situation worse.

    The only reason why some other file systems have chosen to use
    FS_IOC_[GS]ETFLAGS, instead of defining their own ioctl, is so they
    can use lsattr/chattr from e2fsprogs instead of creating their own
    utility. But for statx, there isn't a good reason use the same flags
    number space. At the very least, can we use a new flags field for the
    Windows file attributes? It's not like lsattr/chattr has the ability
    to set those flags today anyway. So we might as well use a new flags
    field and a new flags numberspace for them.

    - Ted


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