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sysfs/kernfs: allow attributes to request write buffer be pre-allocated.

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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>
This commit is contained in:
NeilBrown
2014-10-13 16:41:28 +11:00
committed by Greg Kroah-Hartman
parent 0936896056
commit 2b75869bba
4 changed files with 71 additions and 22 deletions
Download Patch File Download Diff File Expand all files Collapse all files

31
fs/sysfs/file.c
View File

@@ -184,6 +184,17 @@ static const struct kernfs_ops sysfs_file_kfops_rw = {
.write = sysfs_kf_write,
};
static const struct kernfs_ops sysfs_prealloc_kfops_wo = {
.write = sysfs_kf_write,
.prealloc = true,
};
static const struct kernfs_ops sysfs_prealloc_kfops_rw = {
.seq_show = sysfs_kf_seq_show,
.write = sysfs_kf_write,
.prealloc = true,
};
static const struct kernfs_ops sysfs_bin_kfops_ro = {
.read = sysfs_kf_bin_read,
};
@@ -222,13 +233,19 @@ int sysfs_add_file_mode_ns(struct kernfs_node *parent,
kobject_name(kobj)))
return -EINVAL;
if (sysfs_ops->show && sysfs_ops->store)
ops = &sysfs_file_kfops_rw;
else if (sysfs_ops->show)
if (sysfs_ops->show && sysfs_ops->store) {
if (mode & SYSFS_PREALLOC)
ops = &sysfs_prealloc_kfops_rw;
else
ops = &sysfs_file_kfops_rw;
} else if (sysfs_ops->show)
ops = &sysfs_file_kfops_ro;
else if (sysfs_ops->store)
ops = &sysfs_file_kfops_wo;
else
else if (sysfs_ops->store) {
if (mode & SYSFS_PREALLOC)
ops = &sysfs_prealloc_kfops_wo;
else
ops = &sysfs_file_kfops_wo;
} else
ops = &sysfs_file_kfops_empty;
size = PAGE_SIZE;
@@ -253,7 +270,7 @@ int sysfs_add_file_mode_ns(struct kernfs_node *parent,
if (!attr->ignore_lockdep)
key = attr->key ?: (struct lock_class_key *)&attr->skey;
#endif
kn = __kernfs_create_file(parent, attr->name, mode, size, ops,
kn = __kernfs_create_file(parent, attr->name, mode & 0777, size, ops,
(void *)attr, ns, true, key);
if (IS_ERR(kn)) {
if (PTR_ERR(kn) == -EEXIST)