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Message-Id: <20080223000419.d446ac74.akpm@linux-foundation.org>
Date: Sat, 23 Feb 2008 00:04:19 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: menage@...gle.com
Cc: kamezawa.hiroyu@...fujitsu.com, yamamoto@...inux.co.jp,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
balbir@...ibm.com, xemul@...nvz.org
Subject: Re: [PATCH 1/2] cgroup map files: Add cgroup map data type
On Thu, 21 Feb 2008 13:28:55 -0800 menage@...gle.com wrote:
> Adds a new type of supported control file representation, a map from
> strings to u64 values.
>
> The map type is printed in a similar format to /proc/meminfo or
> /proc/<pid>/status, i.e. "$key: $value\n"
>
> Signed-off-by: Paul Menage <menage@...gle.com>
>
> ---
> include/linux/cgroup.h | 19 +++++++++++++++
> kernel/cgroup.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 77 insertions(+), 1 deletion(-)
>
> Index: cgroupmap-2.6.25-rc2-mm1/include/linux/cgroup.h
> ===================================================================
> --- cgroupmap-2.6.25-rc2-mm1.orig/include/linux/cgroup.h
> +++ cgroupmap-2.6.25-rc2-mm1/include/linux/cgroup.h
> @@ -166,6 +166,16 @@ struct css_set {
>
> };
>
> +/*
> + * cgroup_map_cb is an abstract callback API for reporting map-valued
> + * control files
> + */
> +
> +struct cgroup_map_cb {
> + int (*fill)(struct cgroup_map_cb *cb, const char *key, u64 value);
> + void *state;
> +};
> +
> /* struct cftype:
> *
> * The files in the cgroup filesystem mostly have a very simple read/write
> @@ -194,6 +204,15 @@ struct cftype {
> * single integer. Use it in place of read()
> */
> u64 (*read_uint) (struct cgroup *cont, struct cftype *cft);
> + /*
> + * read_map() is used for defining a map of key/value
> + * pairs. It should call cb->fill(cb, key, value) for each
> + * entry. The key/value pairs (and their ordering) should not
> + * change between reboots.
> + */
> + int (*read_map) (struct cgroup *cont, struct cftype *cft,
> + struct cgroup_map_cb *cb);
> +
> ssize_t (*write) (struct cgroup *cont, struct cftype *cft,
> struct file *file,
> const char __user *buf, size_t nbytes, loff_t *ppos);
> Index: cgroupmap-2.6.25-rc2-mm1/kernel/cgroup.c
> ===================================================================
> --- cgroupmap-2.6.25-rc2-mm1.orig/kernel/cgroup.c
> +++ cgroupmap-2.6.25-rc2-mm1/kernel/cgroup.c
> @@ -1487,6 +1487,46 @@ static ssize_t cgroup_file_read(struct f
> return -EINVAL;
> }
>
> +/*
> + * seqfile ops/methods for returning structured data. Currently just
> + * supports string->u64 maps, but can be extended in future.
> + */
> +
> +struct cgroup_seqfile_state {
> + struct cftype *cft;
> + struct cgroup *cgroup;
> +};
> +
> +static int cgroup_map_add(struct cgroup_map_cb *cb, const char *key, u64 value)
> +{
> + struct seq_file *sf = cb->state;
> + return seq_printf(sf, "%s %llu\n", key, value);
> +}
We don't know what type the architecture uses to implement u64. This will
warn on powerpc, sparc64, maybe others.
> +static int cgroup_seqfile_show(struct seq_file *m, void *arg)
> +{
> + struct cgroup_seqfile_state *state = m->private;
> + struct cftype *cft = state->cft;
> + if (cft->read_map) {
> + struct cgroup_map_cb cb = {
> + .fill = cgroup_map_add,
> + .state = m,
> + };
> + return cft->read_map(state->cgroup, cft, &cb);
> + } else {
> + BUG();
That's not really needed. Just call cft->read_map unconditionally. if
it's zero we'll get a null-pointer deref which will have just the same
effect as a BUG.
> + }
> +}
> +
> +int cgroup_seqfile_release(struct inode *inode, struct file *file)
> +{
> + struct seq_file *seq = file->private_data;
> + kfree(seq->private);
> + return single_release(inode, file);
> +}
> +
> +static struct file_operations cgroup_seqfile_operations;
afaict you can just move the definition of cgroup_seqfile_operations here
and avoid the forward decl.
> static int cgroup_file_open(struct inode *inode, struct file *file)
> {
> int err;
> @@ -1499,7 +1539,18 @@ static int cgroup_file_open(struct inode
> cft = __d_cft(file->f_dentry);
> if (!cft)
> return -ENODEV;
> - if (cft->open)
> + if (cft->read_map) {
But above a NULL value is illegal. Why are we testing it here?
> + struct cgroup_seqfile_state *state =
> + kzalloc(sizeof(*state), GFP_USER);
> + if (!state)
> + return -ENOMEM;
> + state->cft = cft;
> + state->cgroup = __d_cgrp(file->f_dentry->d_parent);
> + file->f_op = &cgroup_seqfile_operations;
> + err = single_open(file, cgroup_seqfile_show, state);
> + if (err < 0)
> + kfree(state);
> + } else if (cft->open)
> err = cft->open(inode, file);
> else
> err = 0;
> @@ -1538,6 +1589,12 @@ static struct file_operations cgroup_fil
> .release = cgroup_file_release,
> };
>
> +static struct file_operations cgroup_seqfile_operations = {
> + .read = seq_read,
> + .llseek = seq_lseek,
> + .release = cgroup_seqfile_release,
> +};
> +
> static struct inode_operations cgroup_dir_inode_operations = {
> .lookup = simple_lookup,
> .mkdir = cgroup_mkdir,
>
> --
--
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