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authorNeilBrown <neilb@suse.de>2014-10-13 16:41:28 +1100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-11-07 10:53:25 -0800
commit2b75869bba676c248d8d25ae6d2bd9221dfffdb6 (patch)
treebcbf58a3e4da882e9cc4dda7da4b65f18a01fa81 /include/linux/kernfs.h
parent0936896056365349afa867c16e9f9100a6707cbf (diff)
sysfs/kernfs: allow attributes to request write buffer be pre-allocated.
md/raid allows metadata management to be performed in user-space. A various times, particularly on device failure, the metadata needs to be updated before further writes can be permitted. This means that the user-space program which updates metadata much not block on writeout, and so must not allocate memory. mlockall(MCL_CURRENT|MCL_FUTURE) and pre-allocation can avoid all memory allocation issues for user-memory, but that does not help kernel memory. Several kernel objects can be pre-allocated. e.g. files opened before any writes to the array are permitted. However some kernel allocation happens in places that cannot be pre-allocated. In particular, writes to sysfs files (to tell md that it can now allow writes to the array) allocate a buffer using GFP_KERNEL. This patch allows attributes to be marked as "PREALLOC". In that case the maximal buffer is allocated when the file is opened, and then used on each write instead of allocating a new buffer. As the same buffer is now shared for all writes on the same file description, the mutex is extended to cover full use of the buffer including the copy_from_user(). The new __ATTR_PREALLOC() 'or's a new flag in to the 'mode', which is inspected by sysfs_add_file_mode_ns() to determine if the file should be marked as requiring prealloc. Despite the comment, we *do* use ->seq_show together with ->prealloc in this patch. The next patch fixes that. Signed-off-by: NeilBrown <neilb@suse.de> Reviewed-by: Tejun Heo <tj@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'include/linux/kernfs.h')
-rw-r--r--include/linux/kernfs.h8
1 files changed, 8 insertions, 0 deletions
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 30faf797c2c3..d4e01b358341 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -179,6 +179,7 @@ struct kernfs_open_file {
struct mutex mutex;
int event;
struct list_head list;
+ char *prealloc_buf;
size_t atomic_write_len;
bool mmapped;
@@ -214,6 +215,13 @@ struct kernfs_ops {
* larger ones are rejected with -E2BIG.
*/
size_t atomic_write_len;
+ /*
+ * "prealloc" causes a buffer to be allocated at open for
+ * all read/write requests. As ->seq_show uses seq_read()
+ * which does its own allocation, it is incompatible with
+ * ->prealloc. Provide ->read and ->write with ->prealloc.
+ */
+ bool prealloc;
ssize_t (*write)(struct kernfs_open_file *of, char *buf, size_t bytes,
loff_t off);