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cgroup files: add write_string cgroup control file method 

This patch adds a write_string() method for cgroups control files. The
semantics are that a buffer is copied from userspace to kernelspace
and the handler function invoked on that buffer.  The buffer is
guaranteed to be nul-terminated, and no longer than max_write_len
(defaulting to 64 bytes if unspecified). Later patches will convert
existing raw file write handlers in control group subsystems to use
this method.

Signed-off-by: Paul Menage <menage@google.com>
Cc: Paul Jackson <pj@sgi.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Acked-by: Balbir Singh <balbir@in.ibm.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Paul Menage 2008-07-25 01:46:58 -07:00 committed by Linus Torvalds
parent ce16b49d37
commit db3b14978a
2 changed files with 49 additions and 0 deletions
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14
include/linux/cgroup.h
View File

@ -205,6 +205,13 @@ struct cftype {
* subsystem, followed by a period */
char name[MAX_CFTYPE_NAME];
int private;
/*
* If non-zero, defines the maximum length of string that can
* be passed to write_string; defaults to 64
*/
size_t max_write_len;
int (*open)(struct inode *inode, struct file *file);
ssize_t (*read)(struct cgroup *cgrp, struct cftype *cft,
struct file *file,
@ -248,6 +255,13 @@ struct cftype {
*/
int (*write_s64)(struct cgroup *cgrp, struct cftype *cft, s64 val);
/*
* write_string() is passed a nul-terminated kernelspace
* buffer of maximum length determined by max_write_len.
* Returns 0 or -ve error code.
*/
int (*write_string)(struct cgroup *cgrp, struct cftype *cft,
const char *buffer);
/*
* trigger() callback can be used to get some kick from the
* userspace, when the actual string written is not important

35
kernel/cgroup.c
View File

@ -1363,6 +1363,39 @@ static ssize_t cgroup_write_X64(struct cgroup *cgrp, struct cftype *cft,
return retval;
}
static ssize_t cgroup_write_string(struct cgroup *cgrp, struct cftype *cft,
struct file *file,
const char __user *userbuf,
size_t nbytes, loff_t *unused_ppos)
{
char local_buffer[64];
int retval = 0;
size_t max_bytes = cft->max_write_len;
char *buffer = local_buffer;
if (!max_bytes)
max_bytes = sizeof(local_buffer) - 1;
if (nbytes >= max_bytes)
return -E2BIG;
/* Allocate a dynamic buffer if we need one */
if (nbytes >= sizeof(local_buffer)) {
buffer = kmalloc(nbytes + 1, GFP_KERNEL);
if (buffer == NULL)
return -ENOMEM;
}
if (nbytes && copy_from_user(buffer, userbuf, nbytes))
return -EFAULT;
buffer[nbytes] = 0; /* nul-terminate */
strstrip(buffer);
retval = cft->write_string(cgrp, cft, buffer);
if (!retval)
retval = nbytes;
if (buffer != local_buffer)
kfree(buffer);
return retval;
}
static ssize_t cgroup_common_file_write(struct cgroup *cgrp,
struct cftype *cft,
struct file *file,
@ -1440,6 +1473,8 @@ static ssize_t cgroup_file_write(struct file *file, const char __user *buf,
return cft->write(cgrp, cft, file, buf, nbytes, ppos);
if (cft->write_u64 || cft->write_s64)
return cgroup_write_X64(cgrp, cft, file, buf, nbytes, ppos);
if (cft->write_string)
return cgroup_write_string(cgrp, cft, file, buf, nbytes, ppos);
if (cft->trigger) {
int ret = cft->trigger(cgrp, (unsigned int)cft->private);
return ret ? ret : nbytes;