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author | Tejun Heo <tj@kernel.org> | 2014-02-03 14:09:13 -0500 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2014-02-07 15:52:48 -0800 |
commit | 4d3773c4bb41ed5228f1ab7a4a52b79e17b10515 (patch) | |
tree | 71c30d7009b36d22e9aab816f3dc7e373bb5f1e9 | |
parent | d35258ef702cca0c4e66d799f8e38b78c02ce8a5 (diff) | |
download | op-kernel-dev-4d3773c4bb41ed5228f1ab7a4a52b79e17b10515.zip op-kernel-dev-4d3773c4bb41ed5228f1ab7a4a52b79e17b10515.tar.gz |
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 <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r-- | fs/kernfs/file.c | 49 | ||||
-rw-r--r-- | 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 10a8c91..ddcb471 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 4520c86..47f5235 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); |