On Sat, 1 Sep 2001 Andries.Brouwer@cwi.nl wrote:
> How do you tell when inode is not opened anymore?
> ...
> When do you reset it [i_bcdev]?
>
> Now I see what you are asking - at first I thought you wondered
> about the bookkeeping for the device struct, and there is no problem there,
> but you ask about the bookkeeping for i_bcdev.
>
> Since the refcount is for the device struct, we cannot do anything
> until that count hits zero. Then the release method of the device struct
> is called (which frees it, or decrements a refcount for the module).
Wait a minute. You had suggested (upthread) that these objects are allocated
by partition code and contain per-partition data. Freeing them once the device
is closed looks very odd.
> After this i_bcdev cannot be used anymore.
> Since we don't know whether this happened already, i_bcdev must be
> recomputed on each open or mount.
... and that means that we can't make devfs-like filesystems just set
->i_bdev (or ->i_cdev) at read_super() (or lookup()) and avoid all mess
with major/minor allocation. IMO that's unfortunate, especially since
majors allocation is on the permanent freeze.
> (One might invent additional data structure to avoid this recomputation,
> but data structures take memory and add the complication that they
> must be kept consistent and up-to-date. Since mounting, or opening
> a block device, are very infrequent operations, it does not matter
> that we do a possibly superfluous bdopen().)
Once you look at character devices (they have same set of problems)
frequency goes up big way.
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This archive was generated by hypermail 2b29 : Fri Sep 07 2001 - 21:00:13 EST