[RFC 04/32] fs: introduce sys_newfstat64/sys_newfstatat64

Arnd Bergmann
2014-05-30T20:05:53Z

We want to be able to read file system timestamps beyond year 2038,
which is currently impossibly on 32-bit systems, since none of the
various stat syscall interfaces (oldstat, stat, stat64) handles
correctly.

This introduces a fourth version of the syscalls, called newfstat64
and newfstatat64, which operate on struct newstat64. Each 32-bit
architecture needs to define a version of this structure.
Architectures that have a 64-bit CPU should use the native 64-bit
'struct stat' if possible, so we can avoid adding a compat_newfstatat64
syscall. Note that there is no sys_newlstat64 or sys_newstat64,
as both can be trivially emulated from libc using newfstatat64.

This approach might not be the best solution, as there have been
proposals in the past to add a new 'struct xstat' interface that
would not only solve the y2038 problem but provide a number of
other extensions as well. I have chickened out and avoided reviving
that discussion for now. This new set of syscalls is a much simpler
addition and is hopefully less controversial.
If we end up merging xstat first, we won't need this patch.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
fs/stat.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 55 insertions(+)

diff --git a/fs/stat.c b/fs/stat.c
index ae0c3ce..77fd219 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -445,6 +445,61 @@ SYSCALL_DEFINE4(fstatat64, int, dfd, const char __user *, filename,
}
#endif /* __ARCH_WANT_STAT64 || __ARCH_WANT_COMPAT_STAT64 */

+#ifdef __ARCH_HAS_NEWSTAT64
+/*
+ * we only need this for the native 32-bit path, all architectures should
+ * define the 32-bit newstat64 as compatible with the 64-bit stat or
+ * stat64.
+ */
+static long cp_new_newstat64(struct kstat *stat, struct newstat64 __user *statbuf)
+{
+ struct newstat64 tmp;
+
+ memset(&tmp, 0, sizeof(tmp));
+ tmp.st_dev = huge_encode_dev(stat->dev);
+ tmp.st_rdev = huge_encode_dev(stat->rdev);
+ tmp.st_ino = stat->ino;
+ tmp.st_mode = stat->mode;
+ tmp.st_nlink = stat->nlink;
+ tmp.st_uid = from_kuid_munged(current_user_ns(), stat->uid);
+ tmp.st_gid = from_kgid_munged(current_user_ns(), stat->gid);
+ tmp.st_atime = stat->atime.tv_sec;
+ tmp.st_atime_nsec = stat->atime.tv_nsec;
+ tmp.st_mtime = stat->mtime.tv_sec;
+ tmp.st_mtime_nsec = stat->mtime.tv_nsec;
+ tmp.st_ctime = stat->ctime.tv_sec;
+ tmp.st_ctime_nsec = stat->ctime.tv_nsec;
+ tmp.st_size = stat->size;
+ tmp.st_blocks = stat->blocks;
+ tmp.st_blksize = stat->blksize;
+ return copy_to_user(statbuf,&tmp,sizeof(tmp)) ? -EFAULT : 0;
+}
+
+SYSCALL_DEFINE2(newfstat64, unsigned long, fd, struct newstat64 __user *, statbuf)
+{
+ struct kstat stat;
+ int error;
+
+ error = vfs_fstat(fd, &stat);
+ if (error)
+ return error;
+
+ return cp_new_newstat64(&stat, statbuf);
+}
+
+SYSCALL_DEFINE4(newfstatat64, int, dfd, const char __user *, filename,
+ struct newstat64 __user *, statbuf, int, flag)
+{
+ struct kstat stat;
+ int error;
+
+ error = vfs_fstatat(dfd, filename, &stat, flag);
+ if (error)
+ return error;
+ return cp_new_newstat64(&stat, statbuf);
+}
+#endif
+
/* Caller is here responsible for sufficient locking (ie. inode->i_lock) */
void __inode_add_bytes(struct inode *inode, loff_t bytes)
{
--
1.8.3.2