fdisk

fdisk

[Bruce Dubbs]

In fdisk, printing a partition table gives the headers:

Device Boot      Start         End      Blocks   Id  System

What's a block?  It does not seem to be defined anywhere.  Perhaps an 
update to the man page would be appropriate.  A line in the explanation 
above the partition listing would be even better.

On my system, a block appears to be 2-512 byte sectors, but is it always so?

   -- Bruce

Re: fdisk

[Karel Zak]

On Fri, Jun 24, 2011 at 01:25:39PM -0500, Bruce Dubbs wrote:
> On my system, a block appears to be 2-512 byte sectors, but is it
> always so?

 Yes. It's stupid legacy (the same thing you can found in
 /proc/partitions).

 I hope that one day we will have better and nicer fdisk with 
 human readable sizes ;-)

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com

Re: fdisk

[Mike Frysinger]

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On Monday, June 27, 2011 10:21:19 Karel Zak wrote:
> On Fri, Jun 24, 2011 at 01:25:39PM -0500, Bruce Dubbs wrote:
> > On my system, a block appears to be 2-512 byte sectors, but is it
> > always so?
> 
>  Yes. It's stupid legacy (the same thing you can found in
>  /proc/partitions).
> 
>  I hope that one day we will have better and nicer fdisk with
>  human readable sizes ;-)

and merge duplicated code with cfdisk ;)
-mike

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fdisk

[Bruce Dubbs]

I have a question about (or a enhancement request) running fdisk.  When 
asking to list known partition types, I get about 70 lines of output. 
Generally that would not be a problem, but I was running in a Debian 
install/rescue iso that uses busybox in a 25 line terminal.  I do not 
have a way to scroll up and thus cannot see the first 40 or so partition 
types.

Is there a way to use a pager for this?  In this situation 'more' is 
available but 'less' is not.  Otherwise I think an automatic pause every 
20 lines or so would be appropriate to build into the partition type 
listing.

   -- Bruce Dubbs

Re: fdisk

[Bernhard Voelker]

On 08/31/2015 04:04 AM, Bruce Dubbs wrote:
> I have a question about (or a enhancement request) running fdisk.  When 
> asking to list known partition types, I get about 70 lines of output. 
> Generally that would not be a problem, but I was running in a Debian 
> install/rescue iso that uses busybox in a 25 line terminal.  I do not 
> have a way to scroll up and thus cannot see the first 40 or so partition 
> types.
> 
> Is there a way to use a pager for this?  In this situation 'more' is 
> available but 'less' is not.  Otherwise I think an automatic pause every 
> 20 lines or so would be appropriate to build into the partition type 
> listing.

hmm, I'm getting 27 lines (at a maximum line length of 79 characters) as
output of the 'l' command  here - even if I resize the xterm to 20x80
characters.
OTOH, the main help output via the 'm' command uses 38 lines.  Shouldn't
you also have issues with that one in your environment?

Have a nice day,
Berny

Re: fdisk

[Bruce Dubbs]

Bernhard Voelker wrote:
> On 08/31/2015 04:04 AM, Bruce Dubbs wrote:
>> I have a question about (or a enhancement request) running fdisk.  When
>> asking to list known partition types, I get about 70 lines of output.
>> Generally that would not be a problem, but I was running in a Debian
>> install/rescue iso that uses busybox in a 25 line terminal.  I do not
>> have a way to scroll up and thus cannot see the first 40 or so partition
>> types.
>>
>> Is there a way to use a pager for this?  In this situation 'more' is
>> available but 'less' is not.  Otherwise I think an automatic pause every
>> 20 lines or so would be appropriate to build into the partition type
>> listing.
>
> hmm, I'm getting 27 lines (at a maximum line length of 79 characters) as
> output of the 'l' command  here - even if I resize the xterm to 20x80
> characters.
> OTOH, the main help output via the 'm' command uses 38 lines.  Shouldn't
> you also have issues with that one in your environment?

In a konsole terminal resized to

# echo $LINES
25
# fdisk --version
fdisk from util-linux 2.26.2

Yes, the main menu scrolls off the top do the topmost line is:

n   add a new partition

but that is not a big problem in konsole because I can scroll back the 
buffer.  The l command lists the partition types and the topmost line of 
the screen is entry number 44.

If it's meaningful, for konsole, I do not use a LANG or any LC_* 
variables and the TERM variable is xterm.

The difficult problem is in busybox where there is no scroll back 
capability.

The problem should be relatively easy to reproduce.  Get a copy of 
debian-8.1.0-amd64-DVD-1.iso and boot it either to HW or in a virtual 
system (I'm using qemu).  Follow the prompts and drop to a terminal and 
then run fdisk.

   -- Bruce


   -- Bruce

Re: fdisk

[Isaac Dunham]

On Mon, Aug 31, 2015 at 11:20:24AM -0500, Bruce Dubbs wrote:
> Bernhard Voelker wrote:
> >On 08/31/2015 04:04 AM, Bruce Dubbs wrote:
> >>I have a question about (or a enhancement request) running fdisk.  When
> >>asking to list known partition types, I get about 70 lines of output.
> >>Generally that would not be a problem, but I was running in a Debian
> >>install/rescue iso that uses busybox in a 25 line terminal.  I do not
> >>have a way to scroll up and thus cannot see the first 40 or so partition
> >>types.
> >>
> >>Is there a way to use a pager for this?  In this situation 'more' is
> >>available but 'less' is not.  Otherwise I think an automatic pause every
> >>20 lines or so would be appropriate to build into the partition type
> >>listing.
> >
> >hmm, I'm getting 27 lines (at a maximum line length of 79 characters) as
> >output of the 'l' command  here - even if I resize the xterm to 20x80
> >characters.
> >OTOH, the main help output via the 'm' command uses 38 lines.  Shouldn't
> >you also have issues with that one in your environment?
> 
> In a konsole terminal resized to
> 
> # echo $LINES
> 25
> # fdisk --version
> fdisk from util-linux 2.26.2
> 
> Yes, the main menu scrolls off the top do the topmost line is:
> 
> n   add a new partition
> 
> but that is not a big problem in konsole because I can scroll back the
> buffer.  The l command lists the partition types and the topmost line of the
> screen is entry number 44.
> 
> The difficult problem is in busybox where there is no scroll back
> capability.

If you do not switch VTs, the Linux kernel has a limited "scroll back"
capability:
use <Shift>+<PgUp> or <Shift>+<PgDn>.

There are serious enough limitations to this that it's not really viable
except as a workaround:
-only things that have been on-screen after you last switched to the
current VT will be visible
-switch VTs, and you lose history

But it may be useful to you.

HTH,
Isaac Dunham

Re: fdisk

[Karel Zak]

On Sun, Aug 30, 2015 at 09:04:48PM -0500, Bruce Dubbs wrote:
> I have a question about (or a enhancement request) running fdisk.  When
> asking to list known partition types, I get about 70 lines of output.
> Generally that would not be a problem, but I was running in a Debian
> install/rescue iso that uses busybox in a 25 line terminal.  I do not have a
> way to scroll up and thus cannot see the first 40 or so partition types.
> 
> Is there a way to use a pager for this?  In this situation 'more' is
> available but 'less' is not.  Otherwise I think an automatic pause every 20
> lines or so would be appropriate to build into the partition type listing.

We have lib/pager.c and setup_pager(), but it assumes that the pager
is running all time and maintain stdout until parent process
terminate.

Maybe we can implement something like

 pid = setup_temporary_pager();
    <list partition types>
 close_pager(pid);

as I don't think we want to use pager all time for fdisk. 

Volunteers?:-)

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com

Re: fdisk

[Isaac Dunham]

On Mon, Aug 31, 2015 at 12:06:48PM +0200, Karel Zak wrote:
> On Sun, Aug 30, 2015 at 09:04:48PM -0500, Bruce Dubbs wrote:
> > I have a question about (or a enhancement request) running fdisk.  When
> > asking to list known partition types, I get about 70 lines of output.
> > Generally that would not be a problem, but I was running in a Debian
> > install/rescue iso that uses busybox in a 25 line terminal.  I do not have a
> > way to scroll up and thus cannot see the first 40 or so partition types.
> > 
> > Is there a way to use a pager for this?  In this situation 'more' is
> > available but 'less' is not.  Otherwise I think an automatic pause every 20
> > lines or so would be appropriate to build into the partition type listing.
> 
> We have lib/pager.c and setup_pager(), but it assumes that the pager
> is running all time and maintain stdout until parent process
> terminate.
> 
> Maybe we can implement something like
> 
>  pid = setup_temporary_pager();
>     <list partition types>
>  close_pager(pid);
> 
> as I don't think we want to use pager all time for fdisk. 
> 
> Volunteers?:-)
> 
>     Karel

I'm tempted to volunteer, but I'd like to run something by you first.

I presume that setup_temporary_pager() needs to spawn a pager, with
the pager inheriting stdout/stderr and stdout temporarily redirected
to the pipe, and then close_pager() needs to close the pipe and swap
the old stdout/stderr back in, then wait for pid to exit.

Thus, I'm thinking that the following prototypes would be better:

/* create a pipe, spawn a temporary pager,
 * dup()s fd 1 and possibly fd 2 before redirecting to the pipe
 * if an fd is not dup()'d, set the corresponding duplicate to -1
 */
pid_t setup_temporary_pager(int *dupout, int *duperr);

/* close the pipe, dup2() the saved fds back over fds 1/2,
 * close the duplicates, and wait for the temporary pager to exit
 * if either fd is -1, skip it.
 */
void close_pager(pid, int dupout, int duperr);


setup_temporary_pager will return -1 if it does not spawn the pager
(whether by failure or by PAGER=cat), or if there are problems during
the redirection dance.
It will refuse to spawn a pager if (!isatty(STDOUT_FILENO)).

Does this sound sensible?

Thanks,
Isaac Dunham

Re: fdisk

[Karel Zak]

On Tue, Sep 01, 2015 at 07:07:34PM -0700, Isaac Dunham wrote:
> Thus, I'm thinking that the following prototypes would be better:
> 
> /* create a pipe, spawn a temporary pager,
>  * dup()s fd 1 and possibly fd 2 before redirecting to the pipe
>  * if an fd is not dup()'d, set the corresponding duplicate to -1
>  */
> pid_t setup_temporary_pager(int *dupout, int *duperr);
> 
> /* close the pipe, dup2() the saved fds back over fds 1/2,
>  * close the duplicates, and wait for the temporary pager to exit
>  * if either fd is -1, skip it.
>  */
> void close_pager(pid, int dupout, int duperr);
> 
> 
> setup_temporary_pager will return -1 if it does not spawn the pager
> (whether by failure or by PAGER=cat), or if there are problems during
> the redirection dance.
> It will refuse to spawn a pager if (!isatty(STDOUT_FILENO)).

Yes, on non-tty stdout the both functions have to do nothing.

> Does this sound sensible?

Yes, go ahead.


    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com