Messages in this thread | | | Date | Sat, 1 Sep 2001 22:26:59 +0100 | From | Jamie Lokier <> | Subject | Re: [RFC] lazy allocation of struct block_device |
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Andries.Brouwer@cwi.nl wrote: > From viro@math.psu.edu Sat Sep 1 18:26:53 2001 > > A kdev_t is a pointer to a struct that has the info now found in > > the arrays (and major, minor fields, and a name function..). > > This struct is allocated by the driver. > > Umm... Apply the arguments from the char_device thread - pointers to > unions are rather bad idea. IOW, kdev_t must die - kernel always > knows which kind we are dealing with. >[...] > However, a union is not so bad. It seems a pity to avoid unions > and waste 4 bytes for every inode with separate i_bdev and i_cdev > instead of a single i_bcdev.
Please, a union of different pointer types is much nicer. You can have i_bdev and i_cdev without wasting any bytes.
This form works with GCC 2.96:
union { struct char_device * i_cdev; struct block_device * i_bdev; };
If you're using a really old compiler that doesn't support anonymous unions, (GCC 2.95 might be in this category, I'm not sure), then you'll need this:
#define i_bdev __i_bcdev_union.i_bdev #define i_cdev __i_bcdev_union.i_cdev union { struct char_device * i_cdev; struct block_device * i_bdev; } __i_bcdev_union;
Either way, you avoid pointers to unions and you also avoid having a named union type which contains pointers.
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