[sane-devel] sane_read() parameters

[ky gcp]

Thank you so much for your support allan. I will take note of this.

On Wed, Mar 9, 2016 at 8:17 PM, m. allan noah <kitno455 at gmail.com> wrote:

> Yes- the value of maxlen is determined by the frontend. You cannot
> change it, and you certainly cannot re-alloc. You should have your own
> buffer in the backend, and read bytes from it into the buffer provided
> by the frontend. This type of double buffering will allow you to read
> from the scanner in whatever block size is best, and then respond to
> the frontend however it wants. I recommend that you not make your
> backend buffer very large (to save memory), but you then have to be
> careful not to overflow it when the frontend is draining it slowly.
>
> allan
>
> On Wed, Mar 9, 2016 at 1:14 AM, ky gcp <kygcpsample at gmail.com> wrote:
> > Thank you for such quick response, allan. Do you mean to say that the
> value
> > of maxlen is determined by the frontend? On xsane application, maxlen
> value
> > is 8192 when using acquire preview and then value of maxlen is 65536 when
> > using scan function. Our external backend currently reads images by row
> on
> > sane_read(). Issue occurs when using acquire preview on colored A3
> original
> > because the number of bytes per row is more than the value of maxlen. If
> I
> > reallocate the argument buf to a much bigger size, xsane closes and I get
> > this error message below:
> > *** stack smashing detected ***: xsane terminated
> > Aborted (core dumped)
> >
> > Since our external backend currently reads images by row on sane_read(),
> is
> > it better to just change our implementation on sane_read() ?
> >
> > On Wed, Mar 9, 2016 at 9:39 AM, m. allan noah <kitno455 at gmail.com>
> wrote:
> >>
> >> Because different frontends have different requirements. Some try to
> >> save memory, some try to maximize speed by using large buffers, some
> >> try to fill a network packet exactly. You can (and should expect) to
> >> get any value of maxlen from 1 byte to perhaps a 1M, maybe more.
> >>
> >> allan
> >>
> >> On Tue, Mar 8, 2016 at 8:23 PM, ky gcp <kygcpsample at gmail.com> wrote:
> >> > why does the value of maxlen vary from various frontends?
> >> >
> >> > On Tue, Mar 8, 2016 at 9:06 PM, m. allan noah <kitno455 at gmail.com>
> >> > wrote:
> >> >>
> >> >> maxlen is provided by the caller of the function, to tell the backend
> >> >> how much memory the caller has allocated for image data.
> >> >>
> >> >> allan
> >> >>
> >> >> On Tue, Mar 8, 2016 at 3:09 AM, ky gcp <kygcpsample at gmail.com>
> wrote:
> >> >> > hi,
> >> >> >
> >> >> > how is the argument maxlen determined in sane_read() function?
> >> >> >
> >> >> > SANE_Status sane_read (SANE_Handle h, SANE_Byte * buf, SANE_Int
> >> >> > maxlen,
> >> >> > SANE_Int * len);
> >> >> >
> >> >> > Thanks for your help.
> >> >> >
> >> >> > --
> >> >> > sane-devel mailing list: sane-devel at lists.alioth.debian.org
> >> >> > http://lists.alioth.debian.org/cgi-bin/mailman/listinfo/sane-devel
> >> >> > Unsubscribe: Send mail with subject "unsubscribe your_password"
> >> >> >              to sane-devel-request at lists.alioth.debian.org
> >> >>
> >> >>
> >> >>
> >> >> --
> >> >> "well, I stand up next to a mountain- and I chop it down with the
> edge
> >> >> of my hand"
> >> >
> >> >
> >>
> >>
> >>
> >> --
> >> "well, I stand up next to a mountain- and I chop it down with the edge
> >> of my hand"
> >
> >
>
>
>
> --
> "well, I stand up next to a mountain- and I chop it down with the edge
> of my hand"
>
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