question about fopen fd limit
Lewis Donzis
lew at perftech.com
Tue Dec 27 18:38:28 UTC 2016
I agree, and, in my humble opinion, the FILE structure should never have made any assumptions about the value of an fd, especially that it would fit in a short when an fd is defined as an int. For that matter, fileno() is defined as returning an int, but the implementation is technically returning a short in a non-threaded environment.
I would support changing the __sFILE structure’s _file member to an int and probably also changing _flags to int or unsigned since it would end up getting padded for alignment anyway. It would also be more efficient.
> On Dec 27, 2016, at 12:52 PM, Xin LI <delphij at gmail.com> wrote:
>
> -freebsd-net (bcc), +freebsd-arch
>
> This would work but also comes with a lot of pain.
>
> (But really - why do we implement these accessors, like fileno() and
> friends as macros with knowledge of the sFILE layout? Will it be
> reasonable to start converting these to functions as a first step, which
> would not break ABI but allow us to do it in the future? Otherwise we
> would be just kicking the same can along the street forever...)
>
> FILE is supposed to be fully opaque to application writers in my opinion.
>
> On Sat, Dec 24, 2016 at 5:19 PM, Alfred Perlstein <alfred at freebsd.org>
> wrote:
>
>> Hello 盛慧华
>>
>> Here's another trick that may work.
>>
>> Use funopen(3) and provide your own read/write/seek and close functions
>> for the high fds.
>>
>> You can basically make "cookie" a struct that contains your "int sized"
>> fds.
>>
>> FILE *
>> funopen(const void *cookie, int (*readfn)(void *, char *, int), int
>> (*writefn)(void *, const char *, int),
>> fpos_t (*seekfn)(void *, fpos_t, int), int (*closefn)(void *));
>>
>>
>> If you need more help please make sure to email me directly so I can see
>> your question.
>>
>> -Alfred
>>
>>
>>
>> On 12/23/16 12:48 AM, 盛慧华 wrote:
>>
>>> hi all,
>>>
>>> Thank you for your advice ~
>>> solution 2 definitly broaden my horizons ~~but may be not a good choice
>>> for my project ~~LoL
>>> i will try to mail freebsd-current mail list, if libc is as your
>>> description , may be i should modify it by myself ~~
>>> Thank you so much~
>>> Are u KingSoft's Dr Zhang ? nice to meet you !!!!!
>>>
>>>
>>> winson sheng
>>>
>>>
>>> winson sheng
>>> From: Hongjiang Zhang
>>> Date: 2016-12-23 11:44
>>> To: 盛慧华; freebsd-net
>>> Subject: RE: RE: question about fopen fd limit
>>> Ok. I know.
>>> There are two possible solutions:
>>> Quick solution for short term: modify short to int in libc by yourself,
>>> buildworld and installworld. Pushing to modify libc may take a long time,
>>> especially only few people encounter this issue. You’d better send email to
>>> freebsd-current to confirm whether they accept your suggestion.
>>> Work around: You can first reserve a series of fd before opening TCP
>>> connections. For example, invoke open(“/dev/null”) for 10000 times to get
>>> 10000 fds. Those fd values are small enough to be held by “short”. After
>>> that, start TCP connections. Once you need to fopen a file, please call
>>> open(“xxx”) instead, and then use dup2(old_fd, new_fd) to exchange the two
>>> fd. The old_fd value is the one obtained by open(“xxx”), and new_fd is one
>>> in your reserved fd fields, and next please use fdopen(fd, mode). Here, you
>>> have to manage the reserved fds by yourself including open/close.
>>> In my eyes:
>>> is the quick method, and there is no modifications in your logic.
>>> Needs you to maintain the reserved consecutive fields for fd by yourself,
>>> which increased the complexity of your logic.
>>> Thanks
>>> Hongjiang Zhang
>>> From: 盛慧华 [mailto:hhsheng at corp.netease.com]
>>> Sent: Friday, December 23, 2016 11:02 AM
>>> To: Hongjiang Zhang <honzhan at microsoft.com>; freebsd-net <
>>> freebsd-net at freebsd.org>
>>> Subject: Re: RE: question about fopen fd limit
>>> hi all,
>>> not map TCP to FILE, you misunderstanding my meaning~
>>> for example, if my server tcp already holds 32000 connection
>>> fopen only has 767 fd to use
>>> the problem has no bussiness with tcp fd, BUT fopen ...
>>> in some particular situlations , my server will open 1k+ FILE , that
>>> will exceed the fileno limit, and overflow occur
>>> my server can't open any file more ,that's the problem ~
>>> so i felt if bsd official could change FILE struct's fileno to a
>>> UNSIGNED SHORT that may be an effecient and convenient solution just for my
>>> case ?
>>> UNSIGNED SHORT fileno is enough for me, and i don't wanna change a lot
>>> of FILE function that take FILE * as its argument ~
>>> Thank you ~~~
>>> winson sheng
>>>
>>>
>>> winson sheng
>>> From: Hongjiang Zhang
>>> Date: 2016-12-23 10:17
>>> To: 盛慧华; freebsd-net
>>> Subject: RE: question about fopen fd limit
>>> Why do you need to map TCP fd to FILE?
>>> It is difficult to modify FILE structure. If it is possible, let us
>>> figure out some new designs to meet your requirement.
>>> -----Original Message-----
>>> From: owner-freebsd-net at freebsd.org [mailto:owner-freebsd-net at freebsd.org]
>>> On Behalf Of ???
>>> Sent: Thursday, December 22, 2016 11:57 PM
>>> To: freebsd-net <freebsd-net at freebsd.org>
>>> Subject: question about fopen fd limit
>>> hi all,
>>> hi~
>>> we are from Chinese Game Develop Corp, Netease.
>>> and One of our product using FreeBsd as its OS platform.
>>> This Game has Millions of players online , and Each Server may holds
>>> 25000+ tcp connection at the same time.Thanks to BSD and kqueue :)
>>> for example, it's one of our server , netstat cmd to list
>>> connections overall...
>>> netstat -an | grep 13396 (it's our listening port) | wc -l
>>> 23221
>>> recently we do some performance optimize and promote this connect
>>> limit to 28000+ or 30000+.
>>> But we find Freebsd has a limit that this huge online number will take
>>> 28000+ fd, and bsd FILE * struct's
>>> fd only support to SHORT . such as ..
>>> struct __sFILE {
>>> ...
>>> short _file; /* (*) fileno, if Unix descriptor, else -1 */ ...
>>> so if our server want to fopen some file when we still hold this
>>> online number, the fd amount may easily exceed 32767, and fopen definitely
>>> return a err code. then the server will appear some fataly ERROR.
>>> we do a simple test and confirm this situation.
>>> then in fopen's code , we notice that we can use open to return a fd
>>> instread of fopen to avoid this overflow,
>>> as below
>>> 68 /*
>>> 1 * File descriptors are a full int, but _file is only a short.
>>> 2 * If we get a valid file descriptor that is greater than
>>> 3 * SHRT_MAX, then the fd will get sign-extended into an
>>> 4 * invalid file descriptor. Handle this case by failing the
>>> 5 * open.
>>> 6 */
>>> BUT ... so many c lib FILE series function needs a FILE * pointer
>>> as input argument, we can't convert all of them to fd, or it will be a
>>> rather suffering things to us.
>>> and even in BSD 10 , it seems this short limit still there , but
>>> other OS as debian , FILE strucnt's fileno is a int .
>>> we found an unoffical patch easily change this fileno to unsigned ,
>>> but we are a very stready project, we can't afford the risk to use an
>>> unoffical patch.
>>> so, do you have any plan to change this fopen fd limit to UNSIGNED
>>> SHORT or int in the future ? ushort is enough for us .
>>> if you do , we are really glad and excited~~~~~~~if you don't ,it
>>> donen't matter, plz give us a reply so that we may need to
>>> find some other plan to resolved this suffering thing.
>>> LoL, thank you !!!!!
>>> yours sincerely
>>> winson sheng
>>> winson sheng
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