Missing error values in ftruncate and fallocate man pages?

Missing error values in ftruncate and fallocate man pages?

[Zeno Endemann]

Hello,

I noticed that the man page for truncate(2) does not list the error codes
ENOSPC and EDQUOT, but I would think those should be potentially possible
when actually expanding a file (may depend on file system?).

Similarly, fallocate(2) also does not list EDQUOT (ENOSPC is there however).
Finally, posix_fallocate(3) has no EDQUOT as well, and EIO also seems to be
missing for this one.

Or am I overlooking something?

Thanks,
Zeno Endemann

Re: Missing error values in ftruncate and fallocate man pages?

[Alejandro Colomar]

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Hi Zeno,

On 2026-04-10T18:52:29+0200, Zeno Endemann wrote:
> Hello,
> 
> I noticed that the man page for truncate(2) does not list the error codes
> ENOSPC and EDQUOT, but I would think those should be potentially possible
> when actually expanding a file (may depend on file system?).
> 
> Similarly, fallocate(2) also does not list EDQUOT (ENOSPC is there however).
> Finally, posix_fallocate(3) has no EDQUOT as well, and EIO also seems to be
> missing for this one.
> 
> Or am I overlooking something?

Sounds plausible.  If you could either perform some experiments or show
the relevant kernel sources that make it possible, we could know for
sure.  If you find out it's possible, would you mind sending a patch?


Have a lovely day!
Alex

> 
> Thanks,
> Zeno Endemann
> 
> 

-- 
<https://www.alejandro-colomar.es>

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Re: Missing error values in ftruncate and fallocate man pages?

[Zeno Endemann]

Alejandro Colomar wrote on 10.04.26 19:47:
> Hi Zeno,
> 
> On 2026-04-10T18:52:29+0200, Zeno Endemann wrote:
>> Hello,
>>
>> I noticed that the man page for truncate(2) does not list the error codes
>> ENOSPC and EDQUOT, but I would think those should be potentially possible
>> when actually expanding a file (may depend on file system?).
>>
>> Similarly, fallocate(2) also does not list EDQUOT (ENOSPC is there however).
>> Finally, posix_fallocate(3) has no EDQUOT as well, and EIO also seems to be
>> missing for this one.
>>
>> Or am I overlooking something?
> 
> Sounds plausible.  If you could either perform some experiments or show
> the relevant kernel sources that make it possible, we could know for
> sure.  If you find out it's possible, would you mind sending a patch?

I ran a quick test, on a FAT32 partition ftruncate can indeed return ENOSPC.
On most other file systems I suspect it will not, as most fs support files
with unallocated space. Not sure there is a file system supporting quotas
but not sparse files, I have never worked with quotas. Maybe someone else
can pitch in there?

As a side note, I think it would be preferable if the allowed error codes
would be agreed upon / specified regardless of whether there is an in-kernel
file system which can currently actually return those, since how things are
implemented can change over time, and there is also FUSE - technically with
my own FUSE file system I can make these functions return any arbitrary errno
value, but a well-behaving FUSE implementation of course would restrict itself
to such a specified "contract". Though I suppose this is likely not the right
place to discuss this further ;)

Cheers,


> 
> 
> Have a lovely day!
> Alex
> 
>>
>> Thanks,
>> Zeno Endemann
>>
>>
> 

Re: Missing error values in ftruncate and fallocate man pages?

[Alejandro Colomar]

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Hi Zeno,

On 2026-04-10T21:12:02+0200, Zeno Endemann wrote:
> Alejandro Colomar wrote on 10.04.26 19:47:
> > Hi Zeno,
> > 
> > On 2026-04-10T18:52:29+0200, Zeno Endemann wrote:
> > > Hello,
> > > 
> > > I noticed that the man page for truncate(2) does not list the error codes
> > > ENOSPC and EDQUOT, but I would think those should be potentially possible
> > > when actually expanding a file (may depend on file system?).
> > > 
> > > Similarly, fallocate(2) also does not list EDQUOT (ENOSPC is there however).
> > > Finally, posix_fallocate(3) has no EDQUOT as well, and EIO also seems to be
> > > missing for this one.
> > > 
> > > Or am I overlooking something?
> > 
> > Sounds plausible.  If you could either perform some experiments or show
> > the relevant kernel sources that make it possible, we could know for
> > sure.  If you find out it's possible, would you mind sending a patch?
> 
> I ran a quick test, on a FAT32 partition ftruncate can indeed return ENOSPC.

Thanks!  Would you send a patch?

> On most other file systems I suspect it will not, as most fs support files
> with unallocated space. Not sure there is a file system supporting quotas
> but not sparse files, I have never worked with quotas. Maybe someone else
> can pitch in there?
> 
> As a side note, I think it would be preferable if the allowed error codes
> would be agreed upon / specified regardless of whether there is an in-kernel
> file system which can currently actually return those,

What I'd like is to say "This system call may fail for the same reasons
as <this other>" (plus then a list of syscall-specific errors).  This
would simplify documentation of possible errors, while being much more
accurate.


Have a lovely day!
Alex

> since how things are
> implemented can change over time, and there is also FUSE - technically with
> my own FUSE file system I can make these functions return any arbitrary errno
> value, but a well-behaving FUSE implementation of course would restrict itself
> to such a specified "contract". Though I suppose this is likely not the right
> place to discuss this further ;)
> 
> Cheers,
> 
> 
> > 
> > 
> > Have a lovely day!
> > Alex
> > 
> > > 
> > > Thanks,
> > > Zeno Endemann
> > > 
> > > 
> > 
> 

-- 
<https://www.alejandro-colomar.es>

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