bash usage of fdescfs [was: Re: amd64/188699: Dev tree]

[Jung-uk Kim]

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On 2014-04-21 17:46:32 -0400, Bryan Drewery wrote:
> On 2014-04-21 16:40, Konstantin Belousov wrote:
>> On Mon, Apr 21, 2014 at 05:23:04PM -0400, John Baldwin wrote:
>>> On Monday, April 21, 2014 3:51:33 pm Konstantin Belousov
>>> wrote:
>>>> On Mon, Apr 21, 2014 at 02:31:12PM -0400, John Baldwin
>>>> wrote:
>>>>> On Thursday, April 17, 2014 2:50:01 pm Konstantin Belousov
>>>>> wrote:
>>>>>> The following reply was made to PR amd64/188699; it has
>>>>>> been
>>> noted by GNATS.
>>>>>> 
>>>>>> From: Konstantin Belousov <kostikbel at gmail.com> To: John
>>>>>> Allman <freebsd at hugme.org> Cc:
>>>>>> freebsd-gnats-submit at FreeBSD.org Subject: Re:
>>>>>> amd64/188699: Dev tree Date: Thu, 17 Apr 2014 21:44:52
>>>>>> +0300
>>>>>> 
>>>>>> On Wed, Apr 16, 2014 at 05:32:45PM +0000, John Allman
>>>>>> wrote:
>>>>>>> This is how to reproduce it:
>>>>>>> 
>>>>>>> Fresh install of 10 on AMD 64 install bash `pkg install
>>>>>>> bash` Switch to bash `bash` push a here document into a
>>>>>>> loop: `while true ; do echo;
>>> done< <(echo "123")`
>>>>>>> receive an error: "-su: /dev/fd/62: No such file or
>>>>>>> directory"
>>>>>>> 
>>>>>>> I'm sorry I haven't been able to research this any
>>>>>>> further.
>>> I found how while working on some important matters. As I
>>> mentioned the above works fine in all
>>>>> previous versions of FreeBSD up until 10.
>>>>>>>> How-To-Repeat:
>>>>>>> Fresh install pkg install bash bash while true; do echo
>>>>>>> foo done< <(echo "123")
>>>>>>> 
>>>>>>> -su: /dev/fd/62: No such file or directory
>>>>>> 
>>>>>> So do you have fdescfs mounted on /dev/fd on the machine
>>>>>> where
>>> the
>>>>>> test fails ?  It works for me on head, and if unmounted,
>>>>>> I get
>>> the
>>>>>> same failure message as yours.  I very much doubt that it
>>>>>> has
>>> anything
>>>>>> to do with a system version.
>>>>> 
>>>>> Question I have is why is bash deciding to use /dev/fd/<n>
>>>>> and
>>> require
>>>>> fdescfs?  On older releases bash uses named pipes for this
>>>>> instead.
>>>> 
>>>> The aclocal.m4 contains the test which verifies the presence
>>>> and
>>> usability
>>>> of /dev/fd/n for n>=3 on the _build_ host.  The result of the
>>>> test is used on the installation host afterward.
>>>> 
>>>> Such kinds of bugs are endemic in our ports, but apparently
>>>> upstreams are guilty too.
>>> 
>>> Yuck, yuck.  Should we fix our default package builders to not
>>> mount fdescfs?
>> 
>> IMO, using /dev/fd is more efficient since it avoids pipe inode
>> creation for the 'document here' interpretation.  The /dev/fd is
>> also needed for fexecve(2) to work (with the shebang scripts).
>> Also, I believe that some other high-profile ports require it
>> (OpenJDK ?).
>> 
>> That said, the solution is to have fdescfs mounted on /dev/fd. 
>> This probably should be done by an installer.
> 
> Yup, we mount it mostly for the java ports.

Basically, OpenJDK uses it as poor man's closefrom(2).  If necessary,
we can drop the need for fdescfs from next revision as all supported
FreeBSD versions have it.

Jung-uk Kim
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