Add cgroup write_uint() helper method

Add write_uint() helper method for cgroup subsystems

This helper is analagous to the read_uint() helper method for
reporting u64 values to userspace. It's designed to reduce the amount
of boilerplate requierd for creating new cgroup subsystems.

Signed-off-by: Paul Menage <menage@google.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 e2dd44f..e95143c 100644 (file)
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -125,6 +125,14 @@ struct cftype {
        ssize_t (*write) (struct cgroup *cont, struct cftype *cft,
                          struct file *file,
                          const char __user *buf, size_t nbytes, loff_t *ppos);
+
+       /*
+        * write_uint() is a shortcut for the common case of accepting
+        * a single integer (as parsed by simple_strtoull) from
+        * userspace. Use in place of write(); return 0 or error.
+        */
+       int (*write_uint) (struct cgroup *cont, struct cftype *cft, u64 val);
+
        int (*release) (struct inode *inode, struct file *file);
 };
 

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 356c40d..f4c4dce 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -829,6 +829,39 @@ enum cgroup_filetype {
        FILE_TASKLIST,
 };
 
+static ssize_t cgroup_write_uint(struct cgroup *cont, struct cftype *cft,
+                                struct file *file,
+                                const char __user *userbuf,
+                                size_t nbytes, loff_t *unused_ppos)
+{
+       char buffer[64];
+       int retval = 0;
+       u64 val;
+       char *end;
+
+       if (!nbytes)
+               return -EINVAL;
+       if (nbytes >= sizeof(buffer))
+               return -E2BIG;
+       if (copy_from_user(buffer, userbuf, nbytes))
+               return -EFAULT;
+
+       buffer[nbytes] = 0;     /* nul-terminate */
+
+       /* strip newline if necessary */
+       if (nbytes && (buffer[nbytes-1] == '\n'))
+               buffer[nbytes-1] = 0;
+       val = simple_strtoull(buffer, &end, 0);
+       if (*end)
+               return -EINVAL;
+
+       /* Pass to subsystem */
+       retval = cft->write_uint(cont, cft, val);
+       if (!retval)
+               retval = nbytes;
+       return retval;
+}
+
 static ssize_t cgroup_common_file_write(struct cgroup *cont,
                                           struct cftype *cft,
                                           struct file *file,
@@ -886,10 +919,11 @@ static ssize_t cgroup_file_write(struct file *file, const char __user *buf,
 
        if (!cft)
                return -ENODEV;
-       if (!cft->write)
-               return -EINVAL;
-
-       return cft->write(cont, cft, file, buf, nbytes, ppos);
+       if (cft->write)
+               return cft->write(cont, cft, file, buf, nbytes, ppos);
+       if (cft->write_uint)
+               return cgroup_write_uint(cont, cft, file, buf, nbytes, ppos);
+       return -EINVAL;
 }
 
 static ssize_t cgroup_read_uint(struct cgroup *cont, struct cftype *cft,