Re: [PATCH] fadvise: introduce POSIX_FADV_DONTNEED_FS

On Wed, Apr 27, 2011 at 05:00:12PM +0200, Arnd Bergmann wrote:

On Wednesday 27 April 2011 16:29:05 Andrea Righi wrote:

quoted

diff --git a/include/linux/fadvise.h b/include/linux/fadvise.h
index e8e7471..dc9ce98 100644
--- a/include/linux/fadvise.h
+++ b/include/linux/fadvise.h

@@ -13,9 +13,11 @@
 #if defined(__s390x__)
 #define POSIX_FADV_DONTNEED    6 /* Don't need these pages.  */
 #define POSIX_FADV_NOREUSE     7 /* Data will be accessed once.  */
+#define POSIX_FADV_DONTNEED_FS 8 /* Don't need these filesystem pages.  */
 #else
 #define POSIX_FADV_DONTNEED    4 /* Don't need these pages.  */
 #define POSIX_FADV_NOREUSE     5 /* Data will be accessed once.  */
+#define POSIX_FADV_DONTNEED_FS 6 /* Don't need these filesystem pages.  */
 #endif
 
 #endif /* FADVISE_H_INCLUDED */

Please don't make the s390 mess worse than it already is here.
I think the best solution would be to assign new values starting
from 8 so they can be common for all architectures.

Agreed.

quoted

@@ -127,6 +128,12 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice)
                        invalidate_mapping_pages(mapping, start_index,
                                                end_index);
                break;
+       case POSIX_FADV_DONTNEED_FS:
+               if (!current_euid())
+                       drop_pagecache_sb(file->f_dentry->d_sb, NULL);
+               else
+                       ret = -EPERM;
+               break;

I somewhat disagree with keying the capability off the UID value, even
if that is what the sysctl uses. CAP_SYS_ADMIN is not that nice either, but
I think it's better than the UID here.

OK, I also prefer CAP_SYS_ADMIN.

Aside from these, I like the patch.

	Arnd

I'll wait for other comments and post another version with the changes
you suggested.

Thanks for looking at it.

-Andrea