Re: Minor numbers

Andries.Brouwer
2001-05-14T18:10:11Z

>> The exercise is essentially the patch that I sent last month or so.

> mknod takes a 32bit input
> the stat64 padding only has room for 32bits

Hmm. You make me search for this old patch.
Since Linus' reaction was not exactly positive I left
the topic again, but there must be a copy somewhere..

Aha, found it. Mail from March 24.

==================================================================
...
- For stat all is fine already since we got stat64.
- For mknod a little work is required.
- The state of affairs with loopinfo is sad today (the fact that
kernel and glibc use dev_t of different size causes problems)
but all will be well with 64-bit dev_t.
...
(iii) mknod:
Then there is the prototype of mknod.
I changed it for all filesystems to

diff -r linux-2.4.2/linux/fs/ext2/namei.c linux-2.4.2kdevt/linux/fs/ext2/namei.c
387c387,388
< static int ext2_mknod (struct inode * dir, struct dentry *dentry, int mode, int rdev)
---
> static int ext2_mknod (struct inode * dir, struct dentry *dentry, int mode,
> dev_t rdev)

The system call itself cannot easily be changed to take a larger dev_t,
mostly because under old glibc the high order part would be random.
So, mknod64, with

diff linux-2.4.2/linux/fs/namei.c linux-2.4.2kdevt/linux/fs/namei.c
1205c1208
< asmlinkage long sys_mknod(const char * filename, int mode, dev_t dev)
---
> static long mknod_common(const char * filename, int mode, dev_t dev)
1245a1249,1259
> }
>
> asmlinkage long sys_mknod64(const char * filename, int mode,
> unsigned int ma, unsigned int mi)
> {
> return mknod_common(filename, mode, ((dev_t) ma << 32) | mi);
> }
...
==================================================================

Yes, so mknod is solved by having mknod64.
I saw no problems with stat64, but you do.
Hmm. I was running a system with 64-bit dev_t when I wrote that letter,
so at least for i386 there cannot be any serious problems.
Let me see.

=================== include/asm-i386/stat.h ======================
/* This matches struct stat64 in glibc2.1, hence the absolutely
* insane amounts of padding around dev_t's.
*/
struct stat64 {
unsigned short st_dev;
unsigned char __pad0[10];
...
unsigned short st_rdev;
unsigned char __pad3[10];
...
==================================================================

So, it seems that you are too pessimistic.
The present stat64 structure even allows 96-bit dev_t.

Andries