Re: [RFC 01/15] FS: libfs, implement simple_write_to_buffer

Rafael J. Wysocki
2010-03-23T21:51:01Z

On Tuesday 23 March 2010, Jiri Slaby wrote:
> It will be used in suspend code and serves as an easy wrap around
> copy_from_user. Similar to simple_read_from_buffer, it takes care
> of transfers with proper lengths depending on available and count
> parameters and advances ppos appropriately.
>
> Signed-off-by: Jiri Slaby <jslaby@suse.cz>
> Cc: Nigel Cunningham <ncunningham@crca.org.au>
> Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Cc: linux-fsdevel@vger.kernel.org

Thanks for doing this job, I really appreciate it.

I'll do my best to review the patches in detail later today or tomorrow.

Best,
Rafael

> ---
> fs/libfs.c | 35 +++++++++++++++++++++++++++++++++++
> include/linux/fs.h | 2 ++
> 2 files changed, 37 insertions(+), 0 deletions(-)
>
> diff --git a/fs/libfs.c b/fs/libfs.c
> index 9e50bcf..fda73b3 100644
> --- a/fs/libfs.c
> +++ b/fs/libfs.c
> @@ -546,6 +546,40 @@ ssize_t simple_read_from_buffer(void __user *to, size_t count, loff_t *ppos,
> }
>
> /**
> + * simple_write_to_buffer - copy data from user space to the buffer
> + * @to: the buffer to write to
> + * @available: the size of the buffer
> + * @ppos: the current position in the buffer
> + * @from: the user space buffer to read from
> + * @count: the maximum number of bytes to read
> + *
> + * The simple_write_to_buffer() function reads up to @count bytes from the user
> + * space address starting at @from into the buffer @to at offset @ppos.
> + *
> + * On success, the number of bytes written is returned and the offset @ppos is
> + * advanced by this number, or negative value is returned on error.
> + **/
> +ssize_t simple_write_to_buffer(void *to, size_t available, loff_t *ppos,
> + const void __user *from, size_t count)
> +{
> + loff_t pos = *ppos;
> + size_t ret;
> +
> + if (pos < 0)
> + return -EINVAL;
> + if (pos >= available || !count)
> + return 0;
> + if (count > available - pos)
> + count = available - pos;
> + ret = copy_from_user(to + pos, from, count);
> + if (ret == count)
> + return -EFAULT;
> + count -= ret;
> + *ppos = pos + count;
> + return count;
> +}
> +
> +/**
> * memory_read_from_buffer - copy data from the buffer
> * @to: the kernel space buffer to read to
> * @count: the maximum number of bytes to read
> @@ -863,6 +897,7 @@ EXPORT_SYMBOL(simple_statfs);
> EXPORT_SYMBOL(simple_sync_file);
> EXPORT_SYMBOL(simple_unlink);
> EXPORT_SYMBOL(simple_read_from_buffer);
> +EXPORT_SYMBOL(simple_write_to_buffer);
> EXPORT_SYMBOL(memory_read_from_buffer);
> EXPORT_SYMBOL(simple_transaction_set);
> EXPORT_SYMBOL(simple_transaction_get);
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index a4636b6..0f751b6 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2370,6 +2370,8 @@ extern void simple_release_fs(struct vfsmount **mount, int *count);
>
> extern ssize_t simple_read_from_buffer(void __user *to, size_t count,
> loff_t *ppos, const void *from, size_t available);
> +extern ssize_t simple_write_to_buffer(void *to, size_t available, loff_t *ppos,
> + const void __user *from, size_t count);
>
> extern int simple_fsync(struct file *, struct dentry *, int);
>
>