[Buildroot] sftp-server for use with dropbear?

[Buildroot] sftp-server for use with dropbear?

[Grant Edwards]

Is there any source for an sftp-server for use with dropbear other
than openssh?

[Openssh will no longer build with my libc/toolchain, which is why I
had to switch to using dropbear.]

--
Grant


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Re: [Buildroot] sftp-server for use with dropbear?

[Yann E. MORIN]

Grant, All,

On 2022-09-01 18:41 -0000, Grant Edwards spake thusly:
> Is there any source for an sftp-server for use with dropbear other
> than openssh?

What about gesftpserver, that has been present since Buildroot 2013.02?

Regards,
Yann E. MORIN.

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Re: [Buildroot] sftp-server for use with dropbear?

[Grant Edwards]

On 2022-09-01, Yann E. MORIN <yann.morin.1998@free.fr> wrote:
> Grant, All,
>
> On 2022-09-01 18:41 -0000, Grant Edwards spake thusly:
>> Is there any source for an sftp-server for use with dropbear other
>> than openssh?
>
> What about gesftpserver, that has been present since Buildroot 2013.02?

Thanks! I hadn't spotted that, and none of my Googling led to it
either.

I currently can't select it in "menuconfig" because it requires a
toolchain with wchar support.  I think my (exernal) toolchain does
have wchar support, but apparently buildroot hasn't been told about
it...

--
Grant



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Re: [Buildroot] sftp-server for use with dropbear?

[Yann E. MORIN]

Grant, All,

On 2022-09-01 19:25 -0000, Grant Edwards spake thusly:
> On 2022-09-01, Yann E. MORIN <yann.morin.1998@free.fr> wrote:
> > On 2022-09-01 18:41 -0000, Grant Edwards spake thusly:
> >> Is there any source for an sftp-server for use with dropbear other
> >> than openssh?
> > What about gesftpserver, that has been present since Buildroot 2013.02?
> I currently can't select it in "menuconfig" because it requires a
> toolchain with wchar support.  I think my (exernal) toolchain does
> have wchar support, but apparently buildroot hasn't been told about
> it...

Wchar is optional only for uclibc toolchains; for glibc and musl, wchar
is always available.

If you are using a pre-configured toolchain, that has wchar, but is not
enabled in Buildroot, please send a patch to fix that.

If you are using a custom toolchain, then the conformity of whar is
checked. You must select BR2_TOOLCHAIN_EXTERNAL_WCHAR (or deselect it)
if your toolchain has wchar (or does not have it). Not doing so is going
to result in a buildtime error. See toolchain/helpers.mk, line 306,
which calls check_uclibc_feature, which will error out if the setting is
not correct.

Regards,
Yann E. MORIN.

-- 
.-----------------.--------------------.------------------.--------------------.
|  Yann E. MORIN  | Real-Time Embedded | /"\ ASCII RIBBON | Erics' conspiracy: |
| +33 662 376 056 | Software  Designer | \ / CAMPAIGN     |  ___               |
| +33 561 099 427 `------------.-------:  X  AGAINST      |  \e/  There is no  |
| http://ymorin.is-a-geek.org/ | _/*\_ | / \ HTML MAIL    |   v   conspiracy.  |
'------------------------------^-------^------------------^--------------------'
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Re: [Buildroot] sftp-server for use with dropbear?

[Grant Edwards]

On 2022-09-01, Yann E. MORIN <yann.morin.1998@free.fr> wrote:
>>> What about gesftpserver, that has been present since Buildroot 2013.02?

>> I currently can't select it in "menuconfig" because it requires a
>> toolchain with wchar support.  I think my (exernal) toolchain does
>> have wchar support, but apparently buildroot hasn't been told about
>> it...

Rats. I was wrong. I assumed my toolchain had wchar support because
usr/include/wchar.h existed, but it's a stub:

    $ cat ./arm-unknown-linux-uclibcgnueabi/sysroot/usr/include/wchar.h
    
    /* This wchar.h is used if wchar support is disabled in uClibc.
     * We still want to provide a few basic definitions as the basic
     * C standard requires them.  And it makes our lives easier with
     * no additional overhead.
     */
    ...
    
There's no way I can justify rebuilding the toolchain with uClibc
wchar support enabled for gesftpserver when nothing else in my system
needs wchar support. I'll have to figure out a new test/development
workflow that doesn't use "scp" to copy files onto the target.

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Re: [Buildroot] sftp-server for use with dropbear?

[Grant Edwards]

On 2022-09-01, Grant Edwards <grant.b.edwards@gmail.com> wrote:

> There's no way I can justify rebuilding the toolchain with uClibc
> wchar support enabled for gesftpserver when nothing else in my system
> needs wchar support. I'll have to figure out a new test/development
> workflow that doesn't use "scp" to copy files onto the target.

It looks like the only place wchar support is used is in a couple
spots in sftpclient in the interactive output handling where somebody
is trying to keep things pretty by checking how many display columns
will be occupied by a filename before it's printed using
printf(). [For example in the output of the the "ls" command built in
to the client, it tries to figure out how many columns of filenames to
print, and how to pad them to keep things aligned.]

The server doesn't need wchar support at all.

So the easiest option for me is probably to change the .mk file to
just build/install the server and not the client. I suppose the proper
thing to do would be to change the Config.in file so that building the
client is optional and wchar support is only required when the client
is built.

Or I could patch the client so that if libc doesn't have wchar
support, it assumes that number_of_columns(filename) ==
strlen(filename). People without wchar support who use UTF8 filenames
would have to tolerate columns that don't line up in the output from
the "ls" command.






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Re: [Buildroot] sftp-server for use with dropbear?

[Grant Edwards]

On 2022-09-01, Grant Edwards <grant.b.edwards@gmail.com> wrote:


> The server doesn't need wchar support at all.

I got gesftpserver's server to build without wchar support, and it
works fine. But it's auto-selecting iconv. That makes the total rootfs
size increase for the gesftpserver almost 1MB, and I can't justify
that.

gesftpserver doesn't seem to be well-suited to small target systems
like mine. It would be nice if it could be configured without the
fancy bits for small systems, but maybe that's not allowed by later
versions of the sftp protocol?

--
Grant




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Re: [Buildroot] sftp-server for use with dropbear?

[Grant Edwards]

On 2022-09-01, Grant Edwards <grant.b.edwards@gmail.com> wrote:
> On 2022-09-01, Grant Edwards <grant.b.edwards@gmail.com> wrote:
>
>> The server doesn't need wchar support at all.
>
> I got gesftpserver's server to build without wchar support, and it
> works fine. But it's auto-selecting iconv. That makes the total rootfs
> size increase for the gesftpserver almost 1MB, and I can't justify
> that.

I looked at the iconv use, and it looks like it should be pretty easy
to make iconv a configurable option -- whether that would be accepted
upstream is another question.

But, I finally realized that my problem was triggered by an upgrade to
openssh's "scp" utility v8.8 which uses the SFTP protocol by default
instead of the SCP protocl. [If I wanted to use SFTP, I would have
typed "sftp" not "scp".]  It turns out that with openssh 8.8 "scp -O"
works fine with dropbear. Unfortunately there's no config file or
environment variables for scp like there is for ssh.

--
Grant



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Re: [Buildroot] sftp-server for use with dropbear?

[Thomas Petazzoni via buildroot]

On Thu, 1 Sep 2022 21:48:25 +0200
"Yann E. MORIN" <yann.morin.1998@free.fr> wrote:

> If you are using a custom toolchain, then the conformity of whar is
> checked. You must select BR2_TOOLCHAIN_EXTERNAL_WCHAR (or deselect it)
> if your toolchain has wchar (or does not have it). Not doing so is going
> to result in a buildtime error. See toolchain/helpers.mk, line 306,
> which calls check_uclibc_feature, which will error out if the setting is
> not correct.

I think we also do these checks for non-custom external toolchains, at
least if I recall correctly.

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering and training
https://bootlin.com
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