On Sat, 31 Oct 2009, Ed Schouten wrote:
Turn unused structure fields of cdevsw into spares.
d_uid, d_gid and d_mode are unused, because permissions are stored in
cdevpriv nowadays. d_kind doesn't seem to be used at all. We no longer
keep a list of cdevsw's, so d_list is also unused.
uid_t and gid_t are 32 bits, but mode_t is 16 bits, Because of alignment
constraints of d_kind, we can safely turn it into three 32-bit integers.
d_kind and d_list is equal in size to three pointers.
The underlying change seems fine, especially in -CURRENT, but I'm confused by
the paragraph here on alignment and safety. What do you mean by safe, and
does it matter? From a casual glance (perhaps mistaken), it looks like this
changes the KBI, so all modules declaring struct cdevsw will need to be
rebuilt.
Robert N M Watson
Computer Laboratory
University of Cambridge
Discussed with: kib
Modified:
head/sys/sys/conf.h
Modified: head/sys/sys/conf.h
==============================================================================
--- head/sys/sys/conf.h Sat Oct 31 09:03:48 2009 (r198705)
+++ head/sys/sys/conf.h Sat Oct 31 10:35:41 2009 (r198706)
@@ -210,15 +210,13 @@ struct cdevsw {
d_kqfilter_t *d_kqfilter;
d_purge_t *d_purge;
d_mmap_single_t *d_mmap_single;
- uid_t d_uid;
- gid_t d_gid;
- mode_t d_mode;
- const char *d_kind;
+
+ int32_t d_spare0[3];
+ void *d_spare1[3];
/* These fields should not be messed with by drivers */
- LIST_ENTRY(cdevsw) d_list;
LIST_HEAD(, cdev) d_devs;
- int d_spare3;
+ int d_spare2;
union {
struct cdevsw *gianttrick;
SLIST_ENTRY(cdevsw) postfree_list;
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