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    SubjectRE: [PATCH 4/7] staging: comedi: don't allow read() on async command set up for "write"
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    On Thursday, October 30, 2014 5:42 AM, Ian Abbott wrote:
    > If a Comedi asynchronous command has been set up for data transfer in
    > the "write" direction on the current "read" subdevice (for those
    > subdevices that support both directions), don't allow the "read" file
    > operation as that would mess with the data in the comedi data buffer
    > that is read by the low-level comedi hardware driver.
    >
    > Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
    > ---
    > drivers/staging/comedi/comedi_fops.c | 8 ++++++++
    > 1 file changed, 8 insertions(+)
    >
    > diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
    > index fef68da..6805ec9 100644
    > --- a/drivers/staging/comedi/comedi_fops.c
    > +++ b/drivers/staging/comedi/comedi_fops.c
    > @@ -2210,6 +2210,10 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes,
    > retval = -EACCES;
    > goto out;
    > }
    > + if (async->cmd.flags & CMDF_WRITE) {
    > + retval = -EINVAL;
    > + goto out;
    > + }
    >
    > add_wait_queue(&async->wait_head, &wait);
    > while (nbytes > 0 && !retval) {
    > @@ -2249,6 +2253,10 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes,
    > retval = -EACCES;
    > break;
    > }
    > + if (async->cmd.flags & CMDF_WRITE) {
    > + retval = -EINVAL;
    > + break;
    > + }

    Is this second test really needed in the while() loop?

    For that matter, are the s->busy tests needed in the while() loop?

    > continue;
    > }
    > m = copy_to_user(buf, async->prealloc_buf +

    Regards,
    Hartley



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