[PATCH] fts.3 is not available in LFS builds

[PATCH] fts.3 is not available in LFS builds

[Christoph Hellwig]

As pointed out during a recent discussion on libc-hacker the fts(3)
APIs can't be used with large file offsets:

	https://sourceware.org/bugzilla/show_bug.cgi?id=15838

The manpage should mention this.  Note: the text probably needs some
better formatting at least, but I couldn't come up with proper markup
for compiler arguments.

Signed-off-by: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>

diff --git a/man3/fts.3 b/man3/fts.3
index 9374463..2b14c0d 100644
--- a/man3/fts.3
+++ b/man3/fts.3
@@ -774,6 +774,10 @@ The options were invalid.
 These functions are available in Linux since glibc2.
 .SH CONFORMING TO
 4.4BSD.
+.SH BUGS
+All the APIs described in this manpage are not safe when compiling
+a program using the LFS APIs, e.g. by using
+-D_FILE_OFFSET_BITS=64.
 .\" The following statement is years old, and seems no closer to
 .\" being true -- mtk
 .\" The
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Re: [PATCH] fts.3 is not available in LFS builds

[Michael Kerrisk (man-pages)]

Christoph,

On Sat, Mar 15, 2014 at 2:54 PM, Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org> wrote:
> As pointed out during a recent discussion on libc-hacker the fts(3)
> APIs can't be used with large file offsets:
>
>         https://sourceware.org/bugzilla/show_bug.cgi?id=15838
>
> The manpage should mention this.  Note: the text probably needs some
> better formatting at least, but I couldn't come up with proper markup
> for compiler arguments.
>
> Signed-off-by: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>
>
> diff --git a/man3/fts.3 b/man3/fts.3
> index 9374463..2b14c0d 100644
> --- a/man3/fts.3
> +++ b/man3/fts.3
> @@ -774,6 +774,10 @@ The options were invalid.
>  These functions are available in Linux since glibc2.
>  .SH CONFORMING TO
>  4.4BSD.
> +.SH BUGS
> +All the APIs described in this manpage are not safe when compiling

Should this perhaps better read "not safe on 32-bit systems"?

> +a program using the LFS APIs, e.g. by using
> +-D_FILE_OFFSET_BITS=64.
>  .\" The following statement is years old, and seems no closer to
>  .\" being true -- mtk
>  .\" The
> --
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Cheers,

Michael


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Re: [PATCH] fts.3 is not available in LFS builds

[Christoph Hellwig]

On Sat, Mar 15, 2014 at 03:47:26PM +0100, Michael Kerrisk (man-pages) wrote:
> >  4.4BSD.
> > +.SH BUGS
> > +All the APIs described in this manpage are not safe when compiling
> 
> Should this perhaps better read "not safe on 32-bit systems"?

Well, it works:

 a) on a 32-it system if _FILE_OFFSET_BITS is 32 (currently the default)
 b) on any 64-bit system

Not sure what the best langauge is to communicate this issue to the
user.

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Re: [PATCH] fts.3 is not available in LFS builds

[Michael Kerrisk (man-pages)]

On 03/16/2014 06:22 PM, Christoph Hellwig wrote:
> On Sat, Mar 15, 2014 at 03:47:26PM +0100, Michael Kerrisk (man-pages) wrote:
>>>  4.4BSD.
>>> +.SH BUGS
>>> +All the APIs described in this manpage are not safe when compiling
>>
>> Should this perhaps better read "not safe on 32-bit systems"?
> 
> Well, it works:
> 
>  a) on a 32-it system if _FILE_OFFSET_BITS is 32 (currently the default)
>  b) on any 64-bit system
> 
> Not sure what the best langauge is to communicate this issue to the
> user.
> 
> 

I made it

    BUGS
       All  of  the  APIs described in this man page are not safe when
       compiling a program using the LFS APIs  (e.g.,  when  compiling
       with  -D_FILE_OFFSET_BITS=64).  This means these APIs are unus‐
       able on current 32-bit systems, since those  systems  are  nor‐
       mally built with -D_FILE_OFFSET_BITS=64.


Okay?

Cheers,

Michael


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Re: [PATCH] fts.3 is not available in LFS builds

[Christoph Hellwig]

On Mon, Mar 17, 2014 at 02:56:36PM +0100, Michael Kerrisk (man-pages) wrote:
> I made it
> 
>     BUGS
>        All  of  the  APIs described in this man page are not safe when
>        compiling a program using the LFS APIs  (e.g.,  when  compiling
>        with  -D_FILE_OFFSET_BITS=64).  This means these APIs are unus???
>        able on current 32-bit systems, since those  systems  are  nor???
>        mally built with -D_FILE_OFFSET_BITS=64.

Unfortunately that' not quite true - the default is still
-D_FILE_OFFSET_BITS=32 for the compiler, so you'd need manual action to
change it - which generally is a good idea.

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Re: [PATCH] fts.3 is not available in LFS builds

[Michael Kerrisk (man-pages)]

On Mon, Mar 17, 2014 at 3:01 PM, Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org> wrote:
> On Mon, Mar 17, 2014 at 02:56:36PM +0100, Michael Kerrisk (man-pages) wrote:
>> I made it
>>
>>     BUGS
>>        All  of  the  APIs described in this man page are not safe when
>>        compiling a program using the LFS APIs  (e.g.,  when  compiling
>>        with  -D_FILE_OFFSET_BITS=64).  This means these APIs are unus???
>>        able on current 32-bit systems, since those  systems  are  nor???
>>        mally built with -D_FILE_OFFSET_BITS=64.
>
> Unfortunately that' not quite true - the default is still
> -D_FILE_OFFSET_BITS=32 for the compiler, so you'd need manual action to
> change it - which generally is a good idea.

Oh! I thought most distributors built their 32-bit distros with
-D_FILE_OFFSET_BITS=64 these days? Am I wrong? (I don't have any
32-bit systems handy to sample from.)



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Linux/UNIX System Programming Training: http://man7.org/training/
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Re: [PATCH] fts.3 is not available in LFS builds

[Christoph Hellwig]

On Mon, Mar 17, 2014 at 03:02:53PM +0100, Michael Kerrisk (man-pages) wrote:
> Oh! I thought most distributors built their 32-bit distros with
> -D_FILE_OFFSET_BITS=64 these days? Am I wrong? (I don't have any
> 32-bit systems handy to sample from.)

I think some build systems try to enforce it, but last time Eric Sandeen
checked we still had lots of packages not picking it up.

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Re: [PATCH] fts.3 is not available in LFS builds

[Michael Kerrisk (man-pages)]

On Mon, Mar 17, 2014 at 3:06 PM, Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org> wrote:
> On Mon, Mar 17, 2014 at 03:02:53PM +0100, Michael Kerrisk (man-pages) wrote:
>> Oh! I thought most distributors built their 32-bit distros with
>> -D_FILE_OFFSET_BITS=64 these days? Am I wrong? (I don't have any
>> 32-bit systems handy to sample from.)
>
> I think some build systems try to enforce it, but last time Eric Sandeen
> checked we still had lots of packages not picking it up.

Okay. I trimmed it back close to your original text:

    BUGS
       All  of  the  APIs described in this man page are not safe when
       compiling a program using the LFS APIs on 32-bit systems (e.g.,
       when compiling with -D_FILE_OFFSET_BITS=64).

(Okay?)

Cheers,

Michael


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Re: [PATCH] fts.3 is not available in LFS builds

[Mike Frysinger]

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On Mon 17 Mar 2014 15:11:18 Michael Kerrisk wrote:
> On Mon, Mar 17, 2014 at 3:06 PM, Christoph Hellwig wrote:
> > On Mon, Mar 17, 2014 at 03:02:53PM +0100, Michael Kerrisk wrote:
> >> Oh! I thought most distributors built their 32-bit distros with
> >> -D_FILE_OFFSET_BITS=64 these days? Am I wrong? (I don't have any
> >> 32-bit systems handy to sample from.)
> > 
> > I think some build systems try to enforce it, but last time Eric Sandeen
> > checked we still had lots of packages not picking it up.
> 
> Okay. I trimmed it back close to your original text:
> 
>     BUGS
>        All  of  the  APIs described in this man page are not safe when
>        compiling a program using the LFS APIs on 32-bit systems (e.g.,
>        when compiling with -D_FILE_OFFSET_BITS=64).
> 
> (Okay?)

not to throw a wrench in there as a pedantic a$$hole, but i find the classic 
concept of "32-bit and 64-bit systems" to not really fit into modern world 
(well, it's been this way for much longer, so let's say "mainstream").

would you call all ILP32 ABIs 32-bit ?  e.g. mips' n32 or x86's x32.  
sizeof(long) == 4, but sizeof(off_t) == 8.  POSIX describes these as "ILP32 
OFF64" while the classic 32-bit systems are "ILP32 OFF".

you can (afaik) use -D_FILE_OFFSET_BITS=64 w/x32 and fts.h and have it work.  
maybe we just ignore the issue since fts.h is dead anyways ?  just add a 
section to the fts(3) page recommending people use ftw(3) instead ?
-mike

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Re: [PATCH] fts.3 is not available in LFS builds

[Mike Frysinger]

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On Tue 18 Mar 2014 23:12:45 Mike Frysinger wrote:
> maybe we just ignore the issue since fts.h is dead anyways ?  just add a
> section to the fts(3) page recommending people use ftw(3) instead ?

i might be completely off on fts vs ftw.  there's discussion on glibc lists 
about maybe fixing fts to not suck.  perhaps we just link to the existing bug 
on the topic ?
https://sourceware.org/bugzilla/show_bug.cgi?id=11460
-mike

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Re: [PATCH] fts.3 is not available in LFS builds

[Michael Kerrisk (man-pages)]

On 03/19/2014 04:12 AM, Mike Frysinger wrote:
> On Mon 17 Mar 2014 15:11:18 Michael Kerrisk wrote:
>> On Mon, Mar 17, 2014 at 3:06 PM, Christoph Hellwig wrote:
>>> On Mon, Mar 17, 2014 at 03:02:53PM +0100, Michael Kerrisk wrote:
>>>> Oh! I thought most distributors built their 32-bit distros with
>>>> -D_FILE_OFFSET_BITS=64 these days? Am I wrong? (I don't have any
>>>> 32-bit systems handy to sample from.)
>>>
>>> I think some build systems try to enforce it, but last time Eric Sandeen
>>> checked we still had lots of packages not picking it up.
>>
>> Okay. I trimmed it back close to your original text:
>>
>>     BUGS
>>        All  of  the  APIs described in this man page are not safe when
>>        compiling a program using the LFS APIs on 32-bit systems (e.g.,
>>        when compiling with -D_FILE_OFFSET_BITS=64).
>>
>> (Okay?)
> 
> not to throw a wrench in there as a pedantic a$$hole, but i find the classic 
> concept of "32-bit and 64-bit systems" to not really fit into modern world 
> (well, it's been this way for much longer, so let's say "mainstream").
> 
> would you call all ILP32 ABIs 32-bit ?  e.g. mips' n32 or x86's x32.  
> sizeof(long) == 4, but sizeof(off_t) == 8.  POSIX describes these as "ILP32 
> OFF64" while the classic 32-bit systems are "ILP32 OFF".
> 
> you can (afaik) use -D_FILE_OFFSET_BITS=64 w/x32 and fts.h and have it work.  
> maybe we just ignore the issue since fts.h is dead anyways ?  just add a 
> section to the fts(3) page recommending people use ftw(3) instead ?

Okay, already ;-). I removed the words "on 32-bit systems".


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Re: [PATCH] fts.3 is not available in LFS builds

[Michael Kerrisk (man-pages)]

On 03/19/2014 06:56 AM, Mike Frysinger wrote:
> On Tue 18 Mar 2014 23:12:45 Mike Frysinger wrote:
>> maybe we just ignore the issue since fts.h is dead anyways ?  just add a
>> section to the fts(3) page recommending people use ftw(3) instead ?
> 
> i might be completely off on fts vs ftw.  there's discussion on glibc lists 
> about maybe fixing fts to not suck.  perhaps we just link to the existing bug 
> on the topic ?
> https://sourceware.org/bugzilla/show_bug.cgi?id=11460

Who knows what'll happen. I put a link to that bug in the page source.

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