2008-01-23 22:07:13

by Andrew Morton

Subject: Re: [PATCH 23/49] Add buffer head related helper functions

> On Mon, 21 Jan 2008 22:02:02 -0500 "Theodore Ts'o" <[email protected]> wrote:
> +}
> +EXPORT_SYMBOL(bh_uptodate_or_lock);
> +/**

Missing newline.

> + * bh_submit_read: Submit a locked buffer for reading
> + * @bh: struct buffer_head
> + *
> + * Returns a negative error
> + */
> +int bh_submit_read(struct buffer_head *bh)
> +{
> + if (!buffer_locked(bh))
> + lock_buffer(bh);
> +
> + if (buffer_uptodate(bh))
> + return 0;

Here it can lock the buffer then return zero

> + get_bh(bh);
> + bh->b_end_io = end_buffer_read_sync;
> + submit_bh(READ, bh);
> + wait_on_buffer(bh);
> + if (buffer_uptodate(bh))
> + return 0;

Here it will unlock the buffer and return zero.

This function is unusable when passed an unlocked buffer.

The return value should (always) be documented.

> + return -EIO;
> +}
> +EXPORT_SYMBOL(bh_submit_read);
> void __init buffer_init(void)

Missing newline.

2008-01-24 05:22:41

by Aneesh Kumar K.V

Subject: Re: [PATCH 23/49] Add buffer head related helper functions

On Wed, Jan 23, 2008 at 02:06:48PM -0800, Andrew Morton wrote:
> > On Mon, 21 Jan 2008 22:02:02 -0500 "Theodore Ts'o" <[email protected]> wrote:
> > +}
> > +EXPORT_SYMBOL(bh_uptodate_or_lock);
> > +/**
>
> Missing newline.
>
> > + * bh_submit_read: Submit a locked buffer for reading
> > + * @bh: struct buffer_head
> > + *
> > + * Returns a negative error
> > + */
> > +int bh_submit_read(struct buffer_head *bh)
> > +{
> > + if (!buffer_locked(bh))
> > + lock_buffer(bh);
> > +
> > + if (buffer_uptodate(bh))
> > + return 0;
>
> Here it can lock the buffer then return zero
>
> > + get_bh(bh);
> > + bh->b_end_io = end_buffer_read_sync;
> > + submit_bh(READ, bh);
> > + wait_on_buffer(bh);
> > + if (buffer_uptodate(bh))
> > + return 0;
>
> Here it will unlock the buffer and return zero.
>
> This function is unusable when passed an unlocked buffer.
>

Updated patch below.

commit 70d4ca32604e0935a8b9a49c5ac8b9c64c810693
Author: Aneesh Kumar K.V <[email protected]>
Date: Thu Jan 24 10:50:24 2008 +0530

Add buffer head related helper functions

Add buffer head related helper function bh_uptodate_or_lock and
bh_submit_read which can be used by file system

Signed-off-by: Aneesh Kumar K.V <[email protected]>

diff --git a/fs/buffer.c b/fs/buffer.c
index 7249e01..82aa2db 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -3213,6 +3213,53 @@ static int buffer_cpu_notify(struct notifier_block *self,
return NOTIFY_OK;
}

+/**
+ * bh_uptodate_or_lock: Test whether the buffer is uptodate
+ * @bh: struct buffer_head
+ *
+ * Return true if the buffer is up-to-date and false,
+ * with the buffer locked, if not.
+ */
+int bh_uptodate_or_lock(struct buffer_head *bh)
+{
+ if (!buffer_uptodate(bh)) {
+ lock_buffer(bh);
+ if (!buffer_uptodate(bh))
+ return 0;
+ unlock_buffer(bh);
+ }
+ return 1;
+}
+EXPORT_SYMBOL(bh_uptodate_or_lock);
+
+/**
+ * bh_submit_read: Submit a locked buffer for reading
+ * @bh: struct buffer_head
+ *
+ * Returns zero on success and -EIO on error.If the input
+ * buffer is not locked returns -EINVAL
+ *
+ */
+int bh_submit_read(struct buffer_head *bh)
+{
+ if (!buffer_locked(bh))
+ return -EINVAL;
+
+ if (buffer_uptodate(bh)) {
+ unlock_buffer(bh);
+ return 0;
+ }
+
+ get_bh(bh);
+ bh->b_end_io = end_buffer_read_sync;
+ submit_bh(READ, bh);
+ wait_on_buffer(bh);
+ if (buffer_uptodate(bh))
+ return 0;
+ return -EIO;
+}
+EXPORT_SYMBOL(bh_submit_read);
+
void __init buffer_init(void)
{
int nrpages;
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index da0d83f..e98801f 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -192,6 +192,8 @@ int sync_dirty_buffer(struct buffer_head *bh);
int submit_bh(int, struct buffer_head *);
void write_boundary_block(struct block_device *bdev,
sector_t bblock, unsigned blocksize);
+int bh_uptodate_or_lock(struct buffer_head *bh);
+int bh_submit_read(struct buffer_head *bh);

extern int buffer_heads_over_limit;

2008-01-24 08:54:27

by Andrew Morton

Subject: Re: [PATCH 23/49] Add buffer head related helper functions

> On Thu, 24 Jan 2008 10:52:27 +0530 "Aneesh Kumar K.V" <[email protected]> wrote:
> + * Returns zero on success and -EIO on error.If the input
> + * buffer is not locked returns -EINVAL
> + *
> + */
> +int bh_submit_read(struct buffer_head *bh)
> +{
> + if (!buffer_locked(bh))
> + return -EINVAL;

Is this case just catching a programming bug?

If so, a plain old BUG_ON would be better.