Re: [PATCH v06 33/36] uapi linux/fsmap.h: use __kernel_size_t instead of size_t

On Mon, Aug 07, 2017 at 06:01:43PM +0200, Arnd Bergmann wrote:

On Mon, Aug 7, 2017 at 5:54 PM, Darrick J. Wong [off-list ref] wrote:

quoted

On Sun, Aug 06, 2017 at 06:44:24PM +0200, Mikko Rapeli wrote:

quoted

Fixes user space compilation error:

linux/fsmap.h:71:19: error: unknown type name ‘size_t’
 static __inline__ size_t
                   ^~~~~~

Signed-off-by: Mikko Rapeli <redacted>
Cc: Darrick J. Wong <redacted>
---
 include/uapi/linux/fsmap.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/uapi/linux/fsmap.h b/include/uapi/linux/fsmap.h
index 7e8e5f0bd6d2..99600bbed6b6 100644
--- a/include/uapi/linux/fsmap.h
+++ b/include/uapi/linux/fsmap.h

@@ -68,7 +68,7 @@ struct fsmap_head {
 };

 /* Size of an fsmap_head with room for nr records. */
-static inline size_t
+static inline __kernel_size_t

This is a static inline helper to assist in malloc calls.  We don't pass
size_t to the kernel, so why is this necessary over, say,

#include <sys/types.h>

Either way works, but including a system header from a kernel header
requires an additional "#ifndef __KERNEL__" check, so I think Miko's
variant is a little nicer.

Generally speaking, you also want to avoid including system headers
indirectly from kernel headers, as POSIX requires that including one
system header should not indirectly make symbols from other system
headers visible. I think this is not a problem here though, as no system
header should include linux/fsmap.h.

Sorry, I guess I was a little unclear about what I was asking -- I was
wondering why can't the userspace program include sys/types.h prior to
linux/fsmap.h?  I wasn't proposing including C library headers in kernel
headers.

I think the patch author is pushing towards kernel headers never relying
on /anything/ in the system headers.  For data structures being
exchanged with the kernel I agree, but the fsmap_sizeof result is never
passed to or received from the kernel; it exists purely for malloc
convenience.

--D

         Arnd
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