linux-kernel - [RFC PATCH] vfs: Use 12:20 bit major:minor in stat everywhere

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Date:	Tue,  3 Mar 2015 16:37:00 -0800
From:	Dan Ehrenberg <dehrenberg@...omium.org>
To:	viro@...iv.linux.org.uk, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc:	gwendal@...omium.org, ezequiel@...guardiasur.com.ar,
	Dan Ehrenberg <dehrenberg@...omium.org>
Subject: [RFC PATCH] vfs: Use 12:20 bit major:minor in stat everywhere

Previously, stat on 32-bit platforms used old-style encoding and
validation of major-minor pairs, with 8:8 bits. However, dev_t is
32-bits on these platforms, and coreutils seems to be treating the
values as 12:20 new-style values. The only reason to use the old
version is in the implementation of a legacy filesystem format which
only has 16 bits of space. Communicating a 12:20 value to userspace
when sizeof dev_t == 4 can be done on either a 32-bit or 64-bit
platform.

This patch removes the artificial restriction in major:minor size.
The only backwards incompatibility which results is sometimes stat
succeeds if -EOVERFLOW would be returned otherwise. The legacy
old-style stat call is retained as-is.

Signed-off-by: Dan Ehrenberg <dehrenberg@...omium.org>
---
 fs/stat.c | 15 +++------------
 1 file changed, 3 insertions(+), 12 deletions(-)

diff --git a/fs/stat.c b/fs/stat.c
index ae0c3ce..0a08e83 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -213,15 +213,6 @@ SYSCALL_DEFINE2(fstat, unsigned int, fd, struct __old_kernel_stat __user *, stat
 
 #endif /* __ARCH_WANT_OLD_STAT */
 
-#if BITS_PER_LONG == 32
-#  define choose_32_64(a,b) a
-#else
-#  define choose_32_64(a,b) b
-#endif
-
-#define valid_dev(x)  choose_32_64(old_valid_dev,new_valid_dev)(x)
-#define encode_dev(x) choose_32_64(old_encode_dev,new_encode_dev)(x)
-
 #ifndef INIT_STRUCT_STAT_PADDING
 #  define INIT_STRUCT_STAT_PADDING(st) memset(&st, 0, sizeof(st))
 #endif
@@ -230,7 +221,7 @@ static int cp_new_stat(struct kstat *stat, struct stat __user *statbuf)
 {
 	struct stat tmp;
 
-	if (!valid_dev(stat->dev) || !valid_dev(stat->rdev))
+	if (!new_valid_dev(stat->dev) || !new_valid_dev(stat->rdev))
 		return -EOVERFLOW;
 #if BITS_PER_LONG == 32
 	if (stat->size > MAX_NON_LFS)
@@ -238,7 +229,7 @@ static int cp_new_stat(struct kstat *stat, struct stat __user *statbuf)
 #endif
 
 	INIT_STRUCT_STAT_PADDING(tmp);
-	tmp.st_dev = encode_dev(stat->dev);
+	tmp.st_dev = new_encode_dev(stat->dev);
 	tmp.st_ino = stat->ino;
 	if (sizeof(tmp.st_ino) < sizeof(stat->ino) && tmp.st_ino != stat->ino)
 		return -EOVERFLOW;
@@ -248,7 +239,7 @@ static int cp_new_stat(struct kstat *stat, struct stat __user *statbuf)
 		return -EOVERFLOW;
 	SET_UID(tmp.st_uid, from_kuid_munged(current_user_ns(), stat->uid));
 	SET_GID(tmp.st_gid, from_kgid_munged(current_user_ns(), stat->gid));
-	tmp.st_rdev = encode_dev(stat->rdev);
+	tmp.st_rdev = new_encode_dev(stat->rdev);
 	tmp.st_size = stat->size;
 	tmp.st_atime = stat->atime.tv_sec;
 	tmp.st_mtime = stat->mtime.tv_sec;
-- 
2.2.0.rc0.207.ga3a616c

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