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>
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 88a734e..f537945 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -205,6 +205,13 @@
* 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,
@@ -249,6 +256,13 @@
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
* at all. The private field can be used to determine the
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 70d083c..3a99cc2 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1363,6 +1363,39 @@
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 @@
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;
