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cred/userns: define current_user_ns() as a function 

The current_user_ns() macro currently returns &init_user_ns when user
namespaces are disabled, and that causes several warnings when building
with gcc-6.0 in code that compares the result of the macro to
&init_user_ns itself:

  fs/xfs/xfs_ioctl.c: In function 'xfs_ioctl_setattr_check_projid':
  fs/xfs/xfs_ioctl.c:1249:22: error: self-comparison always evaluates to true [-Werror=tautological-compare]
    if (current_user_ns() == &init_user_ns)

This is a legitimate warning in principle, but here it isn't really
helpful, so I'm reprasing the definition in a way that shuts up the
warning.  Apparently gcc only warns when comparing identical literals,
but it can figure out that the result of an inline function can be
identical to a constant expression in order to optimize a condition yet
not warn about the fact that the condition is known at compile time.
This is exactly what we want here, and it looks reasonable because we
generally prefer inline functions over macros anyway.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Yaowei Bai <baiyaowei@cmss.chinamobile.com>
Cc: James Morris <james.l.morris@oracle.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Arnd Bergmann 2016-03-22 14:27:11 -07:00 committed by Linus Torvalds
parent e8de370188
commit 0335695dfa
2 changed files with 4 additions and 3 deletions
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2
include/linux/capability.h
View File

@ -40,8 +40,6 @@ struct inode;
struct dentry;
struct user_namespace;
struct user_namespace *current_user_ns(void);
extern const kernel_cap_t __cap_empty_set;
extern const kernel_cap_t __cap_init_eff_set;

5
include/linux/cred.h
View File

@ -377,7 +377,10 @@ extern struct user_namespace init_user_ns;
#ifdef CONFIG_USER_NS
#define current_user_ns() (current_cred_xxx(user_ns))
#else
#define current_user_ns() (&init_user_ns)
static inline struct user_namespace *current_user_ns(void)
{
return &init_user_ns;
}
#endif