Messages in this thread | | | Date | Tue, 24 Jun 2008 16:19:23 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 2/8] CGroup Files: Add write_string cgroup control file method |
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On Fri, 20 Jun 2008 16:44:00 -0700 menage@google.com wrote:
> 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);
Everything seems to use size_t (or ssize_t?) except for the ->write_string return value. Can any of this be improved?
> + /* > * 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]; > + 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; > > --
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