From 4d3773c4bb41ed5228f1ab7a4a52b79e17b10515 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 3 Feb 2014 14:09:13 -0500 Subject: [PATCH] kernfs: implement kernfs_ops->atomic_write_len A write to a kernfs_node is buffered through a kernel buffer. Writes <= PAGE_SIZE are performed atomically, while larger ones are executed in PAGE_SIZE chunks. While this is enough for sysfs, cgroup which is scheduled to be converted to use kernfs needs a bit more control over it. This patch adds kernfs_ops->atomic_write_len. If not set (zero), the behavior stays the same. If set, writes upto the size are executed atomically and larger writes are rejected with -E2BIG. A different implementation strategy would be allowing configuring chunking size while making the original write size available to the write method; however, such strategy, while being more complicated, doesn't really buy anything. If the write implementation has to handle chunking, the specific chunk size shouldn't matter all that much. Signed-off-by: Tejun Heo Signed-off-by: Greg Kroah-Hartman --- fs/kernfs/file.c | 49 ++++++++++++++++++++++++++---------------- include/linux/kernfs.h | 8 +++++-- 2 files changed, 37 insertions(+), 20 deletions(-) diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c index 10a8c91c49d6..ddcb471b9cc9 100644 --- a/fs/kernfs/file.c +++ b/fs/kernfs/file.c @@ -252,19 +252,9 @@ static ssize_t kernfs_fop_write(struct file *file, const char __user *user_buf, size_t count, loff_t *ppos) { struct kernfs_open_file *of = kernfs_of(file); - ssize_t len = min_t(size_t, count, PAGE_SIZE); const struct kernfs_ops *ops; - char *buf; - - buf = kmalloc(len + 1, GFP_KERNEL); - if (!buf) - return -ENOMEM; - - if (copy_from_user(buf, user_buf, len)) { - len = -EFAULT; - goto out_free; - } - buf[len] = '\0'; /* guarantee string termination */ + char *buf = NULL; + ssize_t len; /* * @of->mutex nests outside active ref and is just to ensure that @@ -273,22 +263,45 @@ static ssize_t kernfs_fop_write(struct file *file, const char __user *user_buf, mutex_lock(&of->mutex); if (!kernfs_get_active(of->kn)) { mutex_unlock(&of->mutex); - len = -ENODEV; - goto out_free; + return -ENODEV; } ops = kernfs_ops(of->kn); - if (ops->write) - len = ops->write(of, buf, len, *ppos); - else + if (!ops->write) { len = -EINVAL; + goto out_unlock; + } + + if (ops->atomic_write_len) { + len = count; + if (len > ops->atomic_write_len) { + len = -E2BIG; + goto out_unlock; + } + } else { + len = min_t(size_t, count, PAGE_SIZE); + } + + buf = kmalloc(len + 1, GFP_KERNEL); + if (!buf) { + len = -ENOMEM; + goto out_unlock; + } + if (copy_from_user(buf, user_buf, len)) { + len = -EFAULT; + goto out_unlock; + } + buf[len] = '\0'; /* guarantee string termination */ + + len = ops->write(of, buf, len, *ppos); +out_unlock: kernfs_put_active(of->kn); mutex_unlock(&of->mutex); if (len > 0) *ppos += len; -out_free: + kfree(buf); return len; } diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h index 4520c86f5cb4..47f5235a097a 100644 --- a/include/linux/kernfs.h +++ b/include/linux/kernfs.h @@ -178,9 +178,13 @@ struct kernfs_ops { loff_t off); /* - * write() is bounced through kernel buffer and a write larger than - * PAGE_SIZE results in partial operation of PAGE_SIZE. + * write() is bounced through kernel buffer. If atomic_write_len + * is not set, a write larger than PAGE_SIZE results in partial + * operations of PAGE_SIZE chunks. If atomic_write_len is set, + * writes upto the specified size are executed atomically but + * larger ones are rejected with -E2BIG. */ + size_t atomic_write_len; ssize_t (*write)(struct kernfs_open_file *of, char *buf, size_t bytes, loff_t off); -- 2.34.1