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SubjectRe: [PATCH] usb: gadget: ffs: don't allow to open with O_NONBLOCK flag
Date
On Wed, Apr 01 2015, Robert Baldyga <r.baldyga@samsung.com> wrote:
> FunctionFS can't support O_NONBLOCK because read/write operatons are
> directly translated into USB requests which are asynchoronous, so we
> can't know how long we will have to wait for request completion. For
> this reason in case of open with O_NONBLOCK flag we return
> -EWOULDBLOCK.

‘can’t’ is a bit strong of a word here though. It can, but in a few
cases it doesn’t.

It kinda saddens me that this undoes all the lines of code that were put
into the file to support O_NONBLOCK (e.g. FFS_NO_SETUP path of
ffs_ep0_read).

I’m also worried this may break existing applications which, for better
or worse, open the file with O_NONBLOCK.

Most importantly though, this does not stop users from using fcntl to
set O_NONBLOCK, so if you really want to stop O_NONBLOCK from being set,
that path should be checked as well (if possible).

> Signed-off-by: Robert Baldyga <r.baldyga@samsung.com>
> ---
> drivers/usb/gadget/function/f_fs.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
> index 175c995..1014911 100644
> --- a/drivers/usb/gadget/function/f_fs.c
> +++ b/drivers/usb/gadget/function/f_fs.c
> @@ -538,6 +538,14 @@ static int ffs_ep0_open(struct inode *inode, struct file *file)
> if (unlikely(ffs->state == FFS_CLOSING))
> return -EBUSY;
>
> + /*
> + * We are not supporting O_NONBLOCK because read/write operatons are
> + * directly translated into USB requests which are asynchoronous, so
> + * we can't know how long we will have to wait for request completion.
> + */
> + if (unlikely(file->f_flags & O_NONBLOCK))
> + return -EWOULDBLOCK;
> +
> file->private_data = ffs;
> ffs_data_opened(ffs);
>
> @@ -874,6 +882,14 @@ ffs_epfile_open(struct inode *inode, struct file *file)
> if (WARN_ON(epfile->ffs->state != FFS_ACTIVE))
> return -ENODEV;
>
> + /*
> + * We are not supporting O_NONBLOCK because read/write operatons are
> + * directly translated into USB requests which are asynchoronous, so
> + * we can't know how long we will have to wait for request completion.
> + */
> + if (unlikely(file->f_flags & O_NONBLOCK))
> + return -EWOULDBLOCK;
> +
> file->private_data = epfile;
> ffs_data_opened(epfile->ffs);
>
> --
> 1.9.1
>

--
Best regards, _ _
.o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o
..o | Computer Science, Michał “mina86” Nazarewicz (o o)
ooo +--<mpn@google.com>--<xmpp:mina86@jabber.org>--ooO--(_)--Ooo--


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