diff options
author | NeilBrown <neilb@suse.de> | 2014-10-13 16:41:28 +1100 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2014-11-07 10:53:25 -0800 |
commit | 2b75869bba676c248d8d25ae6d2bd9221dfffdb6 (patch) | |
tree | bcbf58a3e4da882e9cc4dda7da4b65f18a01fa81 /include/linux/kernfs.h | |
parent | 0936896056365349afa867c16e9f9100a6707cbf (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.h | 8 |
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); |