Messages in this thread | | | Date | Sat, 23 Feb 2008 00:04:19 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH 1/2] cgroup map files: Add cgroup map data type |
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On Thu, 21 Feb 2008 13:28:55 -0800 menage@google.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@google.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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