Date: Sat, 6 Jun 2015 01:32:57 -0400 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: Making stdio writes robust/recoverable under errors On Fri, Jun 05, 2015 at 11:47:33PM +0200, Laurent Bercot wrote: > On 05/06/2015 23:14, Rich Felker wrote: > >I'm a bit undecided on whether to move forward with this or not. While > >there's some benefit to being able to resume/recover transient errors > >that occur during buffered writing, there are also disadvantages > > My unpopular but firm opinion, which I already have expressed here, is > that stdio is a toy interface that should not be used for any output that > requires the simplest hint of reliability. The loss of information about > the number of bytes actually written when an error occurs is a major > pain point; even if the underlying implementation is as good as can be, > the API is just too poor and it's either fight the interface (in which > case you have already lost), use non-portable extensions (which musl aims > to avoid), or put stdio back into the trash bin and use something else > entirely. > > People who use stdio and expect good behaviour when an error occurs > deserve what's coming at them, and I think that worse is better in this > case: fail as badly as is permitted by the standard instead of trying to > salvage as many scraps as you can. Even if you manage to save a few close > calls, the next crash and burn is just around the corner. So, I vote for > not devoting any more brain power to "stdio robustness" than is strictly > necessary to be standards-compliant. Yes, I'm aware of your position, and while I don't agree with it in general -- there are plenty of cases where the weak control/guarantees stdio gives you are perfectly fine and worth the simplicity and portability the buy you -- I think you're right on this one. I meant to mention that glibc currently behaves like musl does now, at least for regular files. I still think this issue should be kept "open" at least until musl's stdio internals are well-documented, because there might currently be inconsistent behavior with regards to how fmemopen and open_[w]memstream files behave, which should be investigated. But I'm leaning towards not trying to preserve buffer contents after write errors. Rich
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