Re: [patch 09/14] tmpfs: disallow CONFIG_TMPFS_INODE64 on alpha

[Heiko Carstens <hca@linux.ibm.com>]

On Tue, Feb 09, 2021 at 02:03:19PM -0800, Linus Torvalds wrote:
> On Tue, Feb 9, 2021 at 1:42 PM Andrew Morton <akpm@linux-foundation.org> wrote:
> >
> > As with s390, alpha is a 64-bit architecture with a 32-bit ino_t.  With
> > CONFIG_TMPFS_INODE64=y tmpfs mounts will get 64-bit inode numbers and
> > display "inode64" in the mount options, whereas passing "inode64" in the
> > mount options will fail.
> 
> Ugh.
> 
> The two patches for s390 and alpha are obviously the right thing to
> do, but I do wonder if we could strive to make __kernel_ino_t go away
> entirely.
> 
> It's actually not used very much, because it's such a nasty type, and
> s390 and alpha are the only ones that override it from the default
> "word length" version (and honestly, even that default is not a great
> type).
> 
> The main use of it is for "ino_t" and for "struct ustat".
> 
> And yes, "ino_t" is widely used, but I think pretty much all uses of
> it are entirely internal to the kernel, and we could just make it be
> "unsigned long".
> 
> Does anybody see any actual user interfaces that depend on
> "__kernel_ino_t", aka "ino_t" (apart from that "struct ustat")?
> 
> I guess this is mostly a question for s390, which is actively maintained?

I couldn't spot any and also gave the patch below a try and my system
still boots without any errors.
So, as far as I can tell it _should_ be ok to change this.

Note that the unusual 32 bit ino_t also recently caused a bug on
s390. See commit ebce3eb2f7ef ("ceph: fix inode number handling on
arches with 32-bit ino_t"). So getting rid of this would be a good
thing.

diff --git a/arch/Kconfig b/arch/Kconfig
index 24862d15f3a3..383c98e86a70 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -327,6 +327,10 @@ config ARCH_32BIT_OFF_T
 	  still support 32-bit off_t. This option is enabled for all such
 	  architectures explicitly.
 
+# Selected by 64 bit architectures which have a 32 bit f_tinode in struct ustat
+config ARCH_32BIT_USTAT_F_TINODE
+	bool
+
 config HAVE_ASM_MODVERSIONS
 	bool
 	help
diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig
index 1f51437d5765..96ce6565890e 100644
--- a/arch/alpha/Kconfig
+++ b/arch/alpha/Kconfig
@@ -2,6 +2,7 @@
 config ALPHA
 	bool
 	default y
+	select ARCH_32BIT_USTAT_F_TINODE
 	select ARCH_MIGHT_HAVE_PC_PARPORT
 	select ARCH_MIGHT_HAVE_PC_SERIO
 	select ARCH_NO_PREEMPT
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index c72874f09741..434efd9ca0c5 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -58,6 +58,7 @@ config S390
 	# Note: keep this list sorted alphabetically
 	#
 	imply IMA_SECURE_AND_OR_TRUSTED_BOOT
+	select ARCH_32BIT_USTAT_F_TINODE
 	select ARCH_BINFMT_ELF_STATE
 	select ARCH_HAS_DEBUG_VM_PGTABLE
 	select ARCH_HAS_DEBUG_WX
diff --git a/fs/statfs.c b/fs/statfs.c
index 68cb07788750..0ba34c135593 100644
--- a/fs/statfs.c
+++ b/fs/statfs.c
@@ -255,7 +255,10 @@ SYSCALL_DEFINE2(ustat, unsigned, dev, struct ustat __user *, ubuf)
 
 	memset(&tmp,0,sizeof(struct ustat));
 	tmp.f_tfree = sbuf.f_bfree;
-	tmp.f_tinode = sbuf.f_ffree;
+	if (IS_ENABLED(CONFIG_ARCH_32BIT_USTAT_F_TINODE))
+		tmp.f_tinode = min_t(u64, sbuf.f_ffree, UINT_MAX);
+	else
+		tmp.f_tinode = sbuf.f_ffree;
 
 	return copy_to_user(ubuf, &tmp, sizeof(struct ustat)) ? -EFAULT : 0;
 }
diff --git a/include/linux/types.h b/include/linux/types.h
index a147977602b5..1e9d0a2c1dba 100644
--- a/include/linux/types.h
+++ b/include/linux/types.h
@@ -14,7 +14,7 @@ typedef u32 __kernel_dev_t;
 
 typedef __kernel_fd_set		fd_set;
 typedef __kernel_dev_t		dev_t;
-typedef __kernel_ino_t		ino_t;
+typedef __kernel_ulong_t	ino_t;
 typedef __kernel_mode_t		mode_t;
 typedef unsigned short		umode_t;
 typedef u32			nlink_t;
@@ -189,7 +189,11 @@ struct hlist_node {
 
 struct ustat {
 	__kernel_daddr_t	f_tfree;
-	__kernel_ino_t		f_tinode;
+#ifdef ARCH_HAS_32BIT_F_TINODE
+	unsigned int		f_tinode;
+#else
+	unsigned long		f_tinode;
+#endif
 	char			f_fname[6];
 	char			f_fpack[6];
 };