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    SubjectRe: [RFD 1/4] Pass no useless nameidata to the create, lookup, and permission IOPs
    In message <>, writes:
    > The create, lookup, and permission inode operations are all passed a
    > full nameidata. This is unfortunate because in nfsd and the mqueue
    > filesystem, we must instantiate a struct nameidata but cannot provide
    > all of the same information that a regular lookup would provide. The
    > unused fields take up space on the stack, but more importantly, it is
    > not obvious which fields have meaningful values and which don't, and so
    > things might easily break.
    > This patch introduces struct nameidata2 with only the fields that make
    > sense independent of an actual lookup, and uses that struct in those
    > places where a full nameidat is not needed.

    I agree w/ Trond that a better name is needed other than 'nameidata2',
    esp. for something that's a sub-structure (perhaps start it with a '__'?)

    These changes would probably help stackable file systems (e.g., eCryptfs and
    esp. Unionfs) a lot, b/c stackable f/s often call the lower f/s to lookup
    files and such; and in most cases, we just need to pass the intent down, not
    the full VFS-level state info.

    > +/**
    > + * Fields shared between nameidata and nameidata2 -- nameidata2 could
    > + * simply be embedded in nameidata, but then the vfs code would become
    > + * cluttered with dereferences.
    > + */
    > +#define __NAMEIDATA2 \
    > + struct dentry *dentry; \
    > + struct vfsmount *mnt; \
    > + unsigned int flags; \
    > + \
    > + union { \
    > + struct open_intent open; \
    > + } intent;

    Perhaps it is also time to put the dentry + mnt into a single struct path?
    It's a small change, but it emphasizes that the two items here, dentry+mnt,
    really define a single path to be passed around:

    #define __NAMEIDATA \
    struct path path; \
    unsigned int flags; \

    Of course, you'll have to change instances of nd->dentry to nd->path.dentry
    and so on.

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      Last update: 2007-06-27 02:15    [W:0.037 / U:136.072 seconds]
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