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    Subject[PATCH] Add cgroup write_uint() helper method
    Add write_uint() helper method for cgroup subsystems

    This helper is analagous to the read_uint() helper method for
    reporting u64 values to userspace. It's designed to reduce the amount
    of boilerplate requierd for creating new cgroup subsystems.

    Signed-off-by: Paul Menage <menage@google.com>

    ---
    include/linux/cgroup.h | 8 ++++++++
    kernel/cgroup.c | 42 ++++++++++++++++++++++++++++++++++++++----
    2 files changed, 46 insertions(+), 4 deletions(-)

    Index: container-2.6.23-rc8-mm1/include/linux/cgroup.h
    ===================================================================
    --- container-2.6.23-rc8-mm1.orig/include/linux/cgroup.h
    +++ container-2.6.23-rc8-mm1/include/linux/cgroup.h
    @@ -196,6 +196,14 @@ struct cftype {
    ssize_t (*write) (struct cgroup *cont, struct cftype *cft,
    struct file *file,
    const char __user *buf, size_t nbytes, loff_t *ppos);
    +
    + /*
    + * write_uint() is a shortcut for the common case of accepting
    + * a single integer (as parsed by simple_strtoull) from
    + * userspace. Use in place of write(); return 0 or error.
    + */
    + int (*write_uint) (struct cgroup *cont, struct cftype *cft, u64 val);
    +
    int (*release) (struct inode *inode, struct file *file);
    };

    Index: container-2.6.23-rc8-mm1/kernel/cgroup.c
    ===================================================================
    --- container-2.6.23-rc8-mm1.orig/kernel/cgroup.c
    +++ container-2.6.23-rc8-mm1/kernel/cgroup.c
    @@ -1274,6 +1274,39 @@ enum cgroup_filetype {
    FILE_RELEASE_AGENT,
    };

    +static ssize_t cgroup_write_uint(struct cgroup *cont, struct cftype *cft,
    + struct file *file,
    + const char __user *userbuf,
    + size_t nbytes, loff_t *unused_ppos)
    +{
    + char buffer[64];
    + int retval = 0;
    + u64 val;
    + char *end;
    +
    + if (!nbytes)
    + return -EINVAL;
    + if (nbytes >= sizeof(buffer))
    + return -E2BIG;
    + if (copy_from_user(buffer, userbuf, nbytes))
    + return -EFAULT;
    +
    + buffer[nbytes] = 0; /* nul-terminate */
    +
    + /* strip newline if necessary */
    + if (nbytes && (buffer[nbytes-1] == '\n'))
    + buffer[nbytes-1] = 0;
    + val = simple_strtoull(buffer, &end, 0);
    + if (*end)
    + return -EINVAL;
    +
    + /* Pass to subsystem */
    + retval = cft->write_uint(cont, cft, val);
    + if (!retval)
    + retval = nbytes;
    + return retval;
    +}
    +
    static ssize_t cgroup_common_file_write(struct cgroup *cont,
    struct cftype *cft,
    struct file *file,
    @@ -1357,10 +1390,11 @@ static ssize_t cgroup_file_write(struct

    if (!cft)
    return -ENODEV;
    - if (!cft->write)
    - return -EINVAL;
    -
    - return cft->write(cont, cft, file, buf, nbytes, ppos);
    + if (cft->write)
    + return cft->write(cont, cft, file, buf, nbytes, ppos);
    + if (cft->write_uint)
    + return cgroup_write_uint(cont, cft, file, buf, nbytes, ppos);
    + return -EINVAL;
    }

    static ssize_t cgroup_read_uint(struct cgroup *cont, struct cftype *cft,
    -
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