[Qemu-devel] [PATCH] error: fixed error_set_errno() to deal with a negative type of os_error.

[Qemu-devel] [PATCH] error: fixed error_set_errno() to deal with a negative type of os_error.

[SeokYeon Hwang]

Negative type of errno like -ERRNO is used a lot by developers. Therefore, error_set_errno() is modified to deal with a negative type of os_error.
(Negative type is used at pcie_cap_slot_hotplug_common() in hw/pci/pcie.c)

Signed-off-by: SeokYeon Hwang <syeon.hwang@samsung.com>
---
 util/error.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/util/error.c b/util/error.c
index 2ace0d8..5db00c9 100644
--- a/util/error.c
+++ b/util/error.c
@@ -68,7 +68,7 @@ void error_set_errno(Error **errp, int os_errno, ErrorClass err_class,
     va_start(ap, fmt);
     msg1 = g_strdup_vprintf(fmt, ap);
     if (os_errno != 0) {
-        err->msg = g_strdup_printf("%s: %s", msg1, strerror(os_errno));
+        err->msg = g_strdup_printf("%s: %s", msg1, strerror(abs(os_errno)));
         g_free(msg1);
     } else {
         err->msg = msg1;
-- 
2.1.0

Re: [Qemu-devel] [PATCH] error: fixed error_set_errno() to deal with a negative type of os_error.

[Max Reitz]

On 2014-11-05 at 09:09, SeokYeon Hwang wrote:
> Negative type of errno like -ERRNO is used a lot by developers. Therefore, error_set_errno() is modified to deal with a negative type of os_error.
> (Negative type is used at pcie_cap_slot_hotplug_common() in hw/pci/pcie.c)
>
> Signed-off-by: SeokYeon Hwang <syeon.hwang@samsung.com>
> ---
>   util/error.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/util/error.c b/util/error.c
> index 2ace0d8..5db00c9 100644
> --- a/util/error.c
> +++ b/util/error.c
> @@ -68,7 +68,7 @@ void error_set_errno(Error **errp, int os_errno, ErrorClass err_class,
>       va_start(ap, fmt);
>       msg1 = g_strdup_vprintf(fmt, ap);
>       if (os_errno != 0) {
> -        err->msg = g_strdup_printf("%s: %s", msg1, strerror(os_errno));
> +        err->msg = g_strdup_printf("%s: %s", msg1, strerror(abs(os_errno)));
>           g_free(msg1);
>       } else {
>           err->msg = msg1;

This is utterly broken and we should fix all callers instead.

...But I like it.

Reviewed-by: Max Reitz <mreitz@redhat.com>

Re: [Qemu-devel] [PATCH] error: fixed error_set_errno() to deal with a negative type of os_error.

[Paolo Bonzini]

On 05/11/2014 09:12, Max Reitz wrote:
> On 2014-11-05 at 09:09, SeokYeon Hwang wrote:
>> Negative type of errno like -ERRNO is used a lot by developers.
>> Therefore, error_set_errno() is modified to deal with a negative type
>> of os_error.
>> (Negative type is used at pcie_cap_slot_hotplug_common() in
>> hw/pci/pcie.c)
>>
>> Signed-off-by: SeokYeon Hwang <syeon.hwang@samsung.com>
>> ---
>>   util/error.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/util/error.c b/util/error.c
>> index 2ace0d8..5db00c9 100644
>> --- a/util/error.c
>> +++ b/util/error.c
>> @@ -68,7 +68,7 @@ void error_set_errno(Error **errp, int os_errno,
>> ErrorClass err_class,
>>       va_start(ap, fmt);
>>       msg1 = g_strdup_vprintf(fmt, ap);
>>       if (os_errno != 0) {
>> -        err->msg = g_strdup_printf("%s: %s", msg1, strerror(os_errno));
>> +        err->msg = g_strdup_printf("%s: %s", msg1,
>> strerror(abs(os_errno)));
>>           g_free(msg1);
>>       } else {
>>           err->msg = msg1;
> 
> This is utterly broken and we should fix all callers instead.
> 
> ...But I like it.

I don't, we really should fix the callers.

Paolo

> Reviewed-by: Max Reitz <mreitz@redhat.com>

Re: [Qemu-devel] [PATCH] error: fixed error_set_errno() to deal with a negative type of os_error.

[Max Reitz]

On 2014-11-05 at 11:57, Paolo Bonzini wrote:
> On 05/11/2014 09:12, Max Reitz wrote:
>> On 2014-11-05 at 09:09, SeokYeon Hwang wrote:
>>> Negative type of errno like -ERRNO is used a lot by developers.
>>> Therefore, error_set_errno() is modified to deal with a negative type
>>> of os_error.
>>> (Negative type is used at pcie_cap_slot_hotplug_common() in
>>> hw/pci/pcie.c)
>>>
>>> Signed-off-by: SeokYeon Hwang <syeon.hwang@samsung.com>
>>> ---
>>>    util/error.c | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/util/error.c b/util/error.c
>>> index 2ace0d8..5db00c9 100644
>>> --- a/util/error.c
>>> +++ b/util/error.c
>>> @@ -68,7 +68,7 @@ void error_set_errno(Error **errp, int os_errno,
>>> ErrorClass err_class,
>>>        va_start(ap, fmt);
>>>        msg1 = g_strdup_vprintf(fmt, ap);
>>>        if (os_errno != 0) {
>>> -        err->msg = g_strdup_printf("%s: %s", msg1, strerror(os_errno));
>>> +        err->msg = g_strdup_printf("%s: %s", msg1,
>>> strerror(abs(os_errno)));
>>>            g_free(msg1);
>>>        } else {
>>>            err->msg = msg1;
>> This is utterly broken and we should fix all callers instead.
>>
>> ...But I like it.
> I don't, we really should fix the callers.

Of course I understand, but this patch doesn't make matters worse, as 
long as there are not systems which have negative values for errno 
(which I think we generally assume not to exist throughout qemu). That's 
why I'm fine with it. We should fix the callers but I don't see why we 
shouldn't apply this patch as well.

A similar issue already came up and led to commit b276d2499, where 
callers of error_setg_errno() assumed that it would not clobber errno, 
so we fixed some of the callers but also applied that commit which just 
saves errno because there's no reason not to.

Max

> Paolo
>
>> Reviewed-by: Max Reitz <mreitz@redhat.com>

Re: [Qemu-devel] [PATCH] error: fixed error_set_errno() to deal with a negative type of os_error.

[Eric Blake]

[-- Attachment #1: Type: text/plain, Size: 1803 bytes --]

On 11/05/2014 12:11 PM, Max Reitz wrote:

>>>> +        err->msg = g_strdup_printf("%s: %s", msg1,
>>>> strerror(abs(os_errno)));

>> I don't, we really should fix the callers.
> 
> Of course I understand, but this patch doesn't make matters worse, as
> long as there are not systems which have negative values for errno

POSIX requires all defined errno values to be positive; negative errno
values are unambiguous as values that will cause strerror() to have to
generate a message about an unknown value.

> (which I think we generally assume not to exist throughout qemu). That's
> why I'm fine with it. We should fix the callers but I don't see why we
> shouldn't apply this patch as well.

This patch is a bandaid; it makes it harder to find callers that need to
be fixed.  I'd almost argue the exact opposite - add an assert(os_errno
> 0).  Then we'd loudly break on broken callers, making them easier to find.

> 
> A similar issue already came up and led to commit b276d2499, where
> callers of error_setg_errno() assumed that it would not clobber errno,
> so we fixed some of the callers but also applied that commit which just
> saves errno because there's no reason not to.

If we're willing to accept the convenience so that callers can be lazy,
then I like this patch.  If we want to fix bugs in the callers, then
this patch makes it harder to find those bugs.

I'm actually 60:40 in favor of this patch (I think the convenience
outweighs an audit of fixing all callers); but if we do that, then we
might also want to intentionally switch existing callers to pass
negative values rather than declaring that passing a negative value is a
bug.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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Re: [Qemu-devel] [PATCH] error: fixed error_set_errno() to deal with a negative type of os_error.

[Amos Kong]

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On Wed, Nov 05, 2014 at 12:19:34PM +0100, Eric Blake wrote:
> On 11/05/2014 12:11 PM, Max Reitz wrote:
> 
> >>>> +        err->msg = g_strdup_printf("%s: %s", msg1,
> >>>> strerror(abs(os_errno)));
> 
> >> I don't, we really should fix the callers.
> > 
> > Of course I understand, but this patch doesn't make matters worse, as
> > long as there are not systems which have negative values for errno
> 
> POSIX requires all defined errno values to be positive; negative errno
> values are unambiguous as values that will cause strerror() to have to
> generate a message about an unknown value.
> 
> > (which I think we generally assume not to exist throughout qemu). That's
> > why I'm fine with it. We should fix the callers but I don't see why we
> > shouldn't apply this patch as well.
> 
> This patch is a bandaid; it makes it harder to find callers that need to
> be fixed.  I'd almost argue the exact opposite - add an assert(os_errno
> > 0).  Then we'd loudly break on broken callers, making them easier to find.

Agree! use an assert to teach the caller ;)

> > A similar issue already came up and led to commit b276d2499, where
> > callers of error_setg_errno() assumed that it would not clobber errno,
> > so we fixed some of the callers but also applied that commit which just
> > saves errno because there's no reason not to.
> 
> If we're willing to accept the convenience so that callers can be lazy,
> then I like this patch.  If we want to fix bugs in the callers, then
> this patch makes it harder to find those bugs.
> 
> I'm actually 60:40 in favor of this patch (I think the convenience
> outweighs an audit of fixing all callers); but if we do that, then we
> might also want to intentionally switch existing callers to pass
> negative values rather than declaring that passing a negative value is a
> bug.

-- 
			Amos.

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Re: [Qemu-devel] [PATCH] error: fixed error_set_errno() to deal with a negative type of os_error.

[Paolo Bonzini]

On 05/11/2014 12:11, Max Reitz wrote:
> 
> Of course I understand, but this patch doesn't make matters worse, as
> long as there are not systems which have negative values for errno
> (which I think we generally assume not to exist throughout qemu). That's
> why I'm fine with it. We should fix the callers but I don't see why we
> shouldn't apply this patch as well.
> 
> A similar issue already came up and led to commit b276d2499, where
> callers of error_setg_errno() assumed that it would not clobber errno,
> so we fixed some of the callers but also applied that commit which just
> saves errno because there's no reason not to.

I think side effect are a different matter than misuse of QEMU.

There are "only" 157 calls to error_setg_errno; 67 use "errno" as the
argument, and 4 use an explicit errno value (one of them is the wrong
-EBUSY).  The other 86 seem correct and should not be hard to audit.

Let's instead add an assertion check to error_setg_errno.

Paolo

Re: [Qemu-devel] [PATCH] error: fixed error_set_errno() to deal with a negative type of os_error.

[SeokYeon Hwang]

> -----Original Message-----
> From: Paolo Bonzini [mailto:paolo.bonzini@gmail.com] On Behalf Of Paolo
> Bonzini
> Sent: Wednesday, November 05, 2014 9:45 PM
> To: Max Reitz; SeokYeon Hwang; qemu-devel@nongnu.org
> Cc: armbru@redhat.com; paolo.bonzini@gmail.com
> Subject: Re: [PATCH] error: fixed error_set_errno() to deal with a
> negative type of os_error.
> 
> 
> 
> On 05/11/2014 12:11, Max Reitz wrote:
> >
> > Of course I understand, but this patch doesn't make matters worse, as
> > long as there are not systems which have negative values for errno
> > (which I think we generally assume not to exist throughout qemu).
> > That's why I'm fine with it. We should fix the callers but I don't see
> > why we shouldn't apply this patch as well.
> >
> > A similar issue already came up and led to commit b276d2499, where
> > callers of error_setg_errno() assumed that it would not clobber errno,
> > so we fixed some of the callers but also applied that commit which
> > just saves errno because there's no reason not to.
> 
> I think side effect are a different matter than misuse of QEMU.
> 
> There are "only" 157 calls to error_setg_errno; 67 use "errno" as the
> argument, and 4 use an explicit errno value (one of them is the wrong -
> EBUSY).  The other 86 seem correct and should not be hard to audit.
> 
> Let's instead add an assertion check to error_setg_errno.
> 
> Paolo

I have expected to come out several opinions about this patch.

The use of negative errno on "strerror()" was obviously wrong. But that
does not mean it is wrong to use the negative errno on "error_set_errno()".
The reason that I chose this one among the solutions is to change function
specification. I think it seems good to us to respect the tradition of the
developers that use negative errno.

But if error_set_errno() has strict specification - so, we must not change
it's spec - I agree with Paolo's opinion.

Re: [Qemu-devel] [PATCH] error: fixed error_set_errno() to deal with a negative type of os_error.

[Markus Armbruster]

Paolo Bonzini <bonzini@gnu.org> writes:

> On 05/11/2014 12:11, Max Reitz wrote:
>> 
>> Of course I understand, but this patch doesn't make matters worse, as
>> long as there are not systems which have negative values for errno
>> (which I think we generally assume not to exist throughout qemu). That's
>> why I'm fine with it. We should fix the callers but I don't see why we
>> shouldn't apply this patch as well.
>> 
>> A similar issue already came up and led to commit b276d2499, where
>> callers of error_setg_errno() assumed that it would not clobber errno,
>> so we fixed some of the callers but also applied that commit which just
>> saves errno because there's no reason not to.
>
> I think side effect are a different matter than misuse of QEMU.

Yes.

error_setg_errno() had an unclear contract regarding errno.  Some
callers unjustifiedly assumed that it preserves errno.  We clearly
needed to clarify the contract.  Both "preserves" and "doesn't preserve"
make sense.  We picked the one that saves us fixing up callers.

error_setg_errno()'s contract regarding os_error isn't spelled out, but
the general errno contract applies by association: needs to be
non-negative.

> There are "only" 157 calls to error_setg_errno; 67 use "errno" as the
> argument, and 4 use an explicit errno value (one of them is the wrong
> -EBUSY).  The other 86 seem correct and should not be hard to audit.

Negative value is probably just a sign error, but it *could* be a logic
error.  I'd rather not sweep the latter under the carpet.

> Let's instead add an assertion check to error_setg_errno.

Yes, please.

Re: [Qemu-devel] [PATCH] error: fixed error_set_errno() to deal with a negative type of os_error.

[SeokYeon Hwang]

> -----Original Message-----
> From: SeokYeon Hwang [mailto:syeon.hwang@samsung.com]
> Sent: Wednesday, November 05, 2014 10:13 PM
> To: 'Paolo Bonzini'; 'Max Reitz'; 'qemu-devel@nongnu.org'
> Cc: 'armbru@redhat.com'; 'paolo.bonzini@gmail.com'
> Subject: RE: [PATCH] error: fixed error_set_errno() to deal with a
> negative type of os_error.
> 
> > -----Original Message-----
> > From: Paolo Bonzini [mailto:paolo.bonzini@gmail.com] On Behalf Of
> > Paolo Bonzini
> > Sent: Wednesday, November 05, 2014 9:45 PM
> > To: Max Reitz; SeokYeon Hwang; qemu-devel@nongnu.org
> > Cc: armbru@redhat.com; paolo.bonzini@gmail.com
> > Subject: Re: [PATCH] error: fixed error_set_errno() to deal with a
> > negative type of os_error.
> >
> >
> >
> > On 05/11/2014 12:11, Max Reitz wrote:
> > >
> > > Of course I understand, but this patch doesn't make matters worse,
> > > as long as there are not systems which have negative values for
> > > errno (which I think we generally assume not to exist throughout
qemu).
> > > That's why I'm fine with it. We should fix the callers but I don't
> > > see why we shouldn't apply this patch as well.
> > >
> > > A similar issue already came up and led to commit b276d2499, where
> > > callers of error_setg_errno() assumed that it would not clobber
> > > errno, so we fixed some of the callers but also applied that commit
> > > which just saves errno because there's no reason not to.
> >
> > I think side effect are a different matter than misuse of QEMU.
> >
> > There are "only" 157 calls to error_setg_errno; 67 use "errno" as the
> > argument, and 4 use an explicit errno value (one of them is the wrong
> > - EBUSY).  The other 86 seem correct and should not be hard to audit.
> >
> > Let's instead add an assertion check to error_setg_errno.
> >
> > Paolo
> 
> I have expected to come out several opinions about this patch.
> 
> The use of negative errno on "strerror()" was obviously wrong. But that
> does not mean it is wrong to use the negative errno on
"error_set_errno()".
> The reason that I chose this one among the solutions is to change function
> specification. I think it seems good to us to respect the tradition of the
> developers that use negative errno.
> 
> But if error_set_errno() has strict specification - so, we must not change
> it's spec - I agree with Paolo's opinion.

I think we have 2 options.

1. "error_set_errno()" is just utility for developer's convenience.
Why can't we supply more convenience to developer ??
-> My first opinion.

2. It is not just utility function for convenience or we cannot change
its spec because it is well-known function.
-> If this is right, I'm ready to post 2nd patch that applied Paolo's
opinion.

What do you think about it??
Thanks.

Re: [Qemu-devel] [PATCH] error: fixed error_set_errno() to deal with a negative type of os_error.

[Markus Armbruster]

SeokYeon Hwang <syeon.hwang@samsung.com> writes:

>> -----Original Message-----
>> From: SeokYeon Hwang [mailto:syeon.hwang@samsung.com]
>> Sent: Wednesday, November 05, 2014 10:13 PM
>> To: 'Paolo Bonzini'; 'Max Reitz'; 'qemu-devel@nongnu.org'
>> Cc: 'armbru@redhat.com'; 'paolo.bonzini@gmail.com'
>> Subject: RE: [PATCH] error: fixed error_set_errno() to deal with a
>> negative type of os_error.
>> 
>> > -----Original Message-----
>> > From: Paolo Bonzini [mailto:paolo.bonzini@gmail.com] On Behalf Of
>> > Paolo Bonzini
>> > Sent: Wednesday, November 05, 2014 9:45 PM
>> > To: Max Reitz; SeokYeon Hwang; qemu-devel@nongnu.org
>> > Cc: armbru@redhat.com; paolo.bonzini@gmail.com
>> > Subject: Re: [PATCH] error: fixed error_set_errno() to deal with a
>> > negative type of os_error.
>> >
>> >
>> >
>> > On 05/11/2014 12:11, Max Reitz wrote:
>> > >
>> > > Of course I understand, but this patch doesn't make matters worse,
>> > > as long as there are not systems which have negative values for
>> > > errno (which I think we generally assume not to exist throughout
> qemu).
>> > > That's why I'm fine with it. We should fix the callers but I don't
>> > > see why we shouldn't apply this patch as well.
>> > >
>> > > A similar issue already came up and led to commit b276d2499, where
>> > > callers of error_setg_errno() assumed that it would not clobber
>> > > errno, so we fixed some of the callers but also applied that commit
>> > > which just saves errno because there's no reason not to.
>> >
>> > I think side effect are a different matter than misuse of QEMU.
>> >
>> > There are "only" 157 calls to error_setg_errno; 67 use "errno" as the
>> > argument, and 4 use an explicit errno value (one of them is the wrong
>> > - EBUSY).  The other 86 seem correct and should not be hard to audit.
>> >
>> > Let's instead add an assertion check to error_setg_errno.
>> >
>> > Paolo
>> 
>> I have expected to come out several opinions about this patch.
>> 
>> The use of negative errno on "strerror()" was obviously wrong. But that
>> does not mean it is wrong to use the negative errno on
> "error_set_errno()".
>> The reason that I chose this one among the solutions is to change function
>> specification. I think it seems good to us to respect the tradition of the
>> developers that use negative errno.
>> 
>> But if error_set_errno() has strict specification - so, we must not change
>> it's spec - I agree with Paolo's opinion.
>
> I think we have 2 options.
>
> 1. "error_set_errno()" is just utility for developer's convenience.
> Why can't we supply more convenience to developer ??
> -> My first opinion.
>
> 2. It is not just utility function for convenience or we cannot change
> its spec because it is well-known function.
> -> If this is right, I'm ready to post 2nd patch that applied Paolo's
> opinion.
>
> What do you think about it??

3. Passing a negative value to an errno parameter is wrong.  It's
probably a harmless sign error, but it *could* be a logic error.  We
should not sweep programming errors under the rug.

Please assert(os_error >= 0).  Help with auditing callers is welcome.

Re: [Qemu-devel] [PATCH] error: fixed error_set_errno() to deal with a negative type of os_error.

[SeokYeon Hwang]

> -----Original Message-----
> From: Markus Armbruster [mailto:armbru@redhat.com]
> Sent: Thursday, November 06, 2014 6:25 PM
> To: SeokYeon Hwang
> Cc: 'Paolo Bonzini'; 'Max Reitz'; qemu-devel@nongnu.org; Peter Maydell;
> paolo.bonzini@gmail.com
> Subject: Re: [Qemu-devel] [PATCH] error: fixed error_set_errno() to deal
> with a negative type of os_error.
> 
> SeokYeon Hwang <syeon.hwang@samsung.com> writes:
> 
> >> -----Original Message-----
> >> From: SeokYeon Hwang [mailto:syeon.hwang@samsung.com]
> >> Sent: Wednesday, November 05, 2014 10:13 PM
> >> To: 'Paolo Bonzini'; 'Max Reitz'; 'qemu-devel@nongnu.org'
> >> Cc: 'armbru@redhat.com'; 'paolo.bonzini@gmail.com'
> >> Subject: RE: [PATCH] error: fixed error_set_errno() to deal with a
> >> negative type of os_error.
> >>
> >> > -----Original Message-----
> >> > From: Paolo Bonzini [mailto:paolo.bonzini@gmail.com] On Behalf Of
> >> > Paolo Bonzini
> >> > Sent: Wednesday, November 05, 2014 9:45 PM
> >> > To: Max Reitz; SeokYeon Hwang; qemu-devel@nongnu.org
> >> > Cc: armbru@redhat.com; paolo.bonzini@gmail.com
> >> > Subject: Re: [PATCH] error: fixed error_set_errno() to deal with a
> >> > negative type of os_error.
> >> >
> >> >
> >> >
> >> > On 05/11/2014 12:11, Max Reitz wrote:
> >> > >
> >> > > Of course I understand, but this patch doesn't make matters
> >> > > worse, as long as there are not systems which have negative
> >> > > values for errno (which I think we generally assume not to exist
> >> > > throughout
> > qemu).
> >> > > That's why I'm fine with it. We should fix the callers but I
> >> > > don't see why we shouldn't apply this patch as well.
> >> > >
> >> > > A similar issue already came up and led to commit b276d2499,
> >> > > where callers of error_setg_errno() assumed that it would not
> >> > > clobber errno, so we fixed some of the callers but also applied
> >> > > that commit which just saves errno because there's no reason not
to.
> >> >
> >> > I think side effect are a different matter than misuse of QEMU.
> >> >
> >> > There are "only" 157 calls to error_setg_errno; 67 use "errno" as
> >> > the argument, and 4 use an explicit errno value (one of them is the
> >> > wrong
> >> > - EBUSY).  The other 86 seem correct and should not be hard to audit.
> >> >
> >> > Let's instead add an assertion check to error_setg_errno.
> >> >
> >> > Paolo
> >>
> >> I have expected to come out several opinions about this patch.
> >>
> >> The use of negative errno on "strerror()" was obviously wrong. But
> >> that does not mean it is wrong to use the negative errno on
> > "error_set_errno()".
> >> The reason that I chose this one among the solutions is to change
> >> function specification. I think it seems good to us to respect the
> >> tradition of the developers that use negative errno.
> >>
> >> But if error_set_errno() has strict specification - so, we must not
> >> change it's spec - I agree with Paolo's opinion.
> >
> > I think we have 2 options.
> >
> > 1. "error_set_errno()" is just utility for developer's convenience.
> > Why can't we supply more convenience to developer ??
> > -> My first opinion.
> >
> > 2. It is not just utility function for convenience or we cannot change
> > its spec because it is well-known function.
> > -> If this is right, I'm ready to post 2nd patch that applied Paolo's
> > opinion.
> >
> > What do you think about it??
> 
> 3. Passing a negative value to an errno parameter is wrong.  It's probably
> a harmless sign error, but it *could* be a logic error.  We should not
> sweep programming errors under the rug.
> 
> Please assert(os_error >= 0).  Help with auditing callers is welcome.

I just posted patch v2.
Thank you for your advice.