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cgroup files: add write_string cgroup control file method
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> Cc: Paul Jackson <pj@sgi.com> Cc: Pavel Emelyanov <xemul@openvz.org> Acked-by: Balbir Singh <balbir@in.ibm.com> Acked-by: Serge Hallyn <serue@us.ibm.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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2 changed files with 49 additions and 0 deletions
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@ -205,6 +205,13 @@ struct cftype {
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* subsystem, followed by a period */
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char name[MAX_CFTYPE_NAME];
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int private;
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/*
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* If non-zero, defines the maximum length of string that can
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* be passed to write_string; defaults to 64
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*/
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size_t max_write_len;
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int (*open)(struct inode *inode, struct file *file);
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ssize_t (*read)(struct cgroup *cgrp, struct cftype *cft,
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struct file *file,
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@ -248,6 +255,13 @@ struct cftype {
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*/
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int (*write_s64)(struct cgroup *cgrp, struct cftype *cft, s64 val);
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/*
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* write_string() is passed a nul-terminated kernelspace
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* buffer of maximum length determined by max_write_len.
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* Returns 0 or -ve error code.
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*/
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int (*write_string)(struct cgroup *cgrp, struct cftype *cft,
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const char *buffer);
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/*
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* trigger() callback can be used to get some kick from the
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* userspace, when the actual string written is not important
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