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SubjectRe: [PATCH 2/8] CGroup Files: Add write_string cgroup control file method
* menage@google.com <menage@google.com> [2008-06-20 16:44:00]:

> 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>
>
> ---
> include/linux/cgroup.h | 14 ++++++++++++++
> kernel/cgroup.c | 35 +++++++++++++++++++++++++++++++++++
> 2 files changed, 49 insertions(+)
>
> Index: cws-2.6.26-rc5-mm3/include/linux/cgroup.h
> ===================================================================
> --- cws-2.6.26-rc5-mm3.orig/include/linux/cgroup.h
> +++ cws-2.6.26-rc5-mm3/include/linux/cgroup.h
> @@ -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,
> @@ -249,6 +256,13 @@ 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
> * at all. The private field can be used to determine the
> Index: cws-2.6.26-rc5-mm3/kernel/cgroup.c
> ===================================================================
> --- cws-2.6.26-rc5-mm3.orig/kernel/cgroup.c
> +++ cws-2.6.26-rc5-mm3/kernel/cgroup.c
> @@ -1363,6 +1363,39 @@ static ssize_t cgroup_write_X64(struct c
> 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];

64? a define would be more meaningful

> + 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
> 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;
>
> --


Looks good

Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>

--
Warm Regards,
Balbir Singh
Linux Technology Center
IBM, ISTL


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