Date: Mon, 03 Nov 2014 16:23:35 +0800 From: Julian Elischer <julian@freebsd.org> To: Mateusz Guzik <mjg@FreeBSD.org>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r274017 - head/sys/kern Message-ID: <54573B87.7000801@freebsd.org> In-Reply-To: <54573AEE.9010602@freebsd.org> References: <201411030746.sA37kpPu037113@svn.freebsd.org> <54573AEE.9010602@freebsd.org>
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On 11/3/14, 4:21 PM, Julian Elischer wrote: > On 11/3/14, 3:46 PM, Mateusz Guzik wrote: >> Author: mjg >> Date: Mon Nov 3 07:46:51 2014 >> New Revision: 274017 >> URL: https://svnweb.freebsd.org/changeset/base/274017 >> >> Log: >> Provide an on-stack temporary buffer for small ioctl requests. > I'm not sure I like this. We don't know how many more levels > of stack may be needed. > I know that machines are getting faster with more memory, > but the current move towards bloating out the ... "bloating out the stack" ... > worries me. we started out with a single page of stack (SHARED > with the U-area!). I think we are now at several pages.. I forget, > is it 8? > I'm open to being persuaded but I think we need to have a discussion > about stack usage. We used to say that anything greater that, say > 64 bytes should probably be allocated. > >> Modified: >> head/sys/kern/sys_generic.c >> >> Modified: head/sys/kern/sys_generic.c >> ============================================================================== >> >> --- head/sys/kern/sys_generic.c Mon Nov 3 07:18:42 2014 (r274016) >> +++ head/sys/kern/sys_generic.c Mon Nov 3 07:46:51 2014 (r274017) >> @@ -649,6 +649,7 @@ sys_ioctl(struct thread *td, struct ioct >> u_long com; >> int arg, error; >> u_int size; >> + u_char smalldata[128]; >> caddr_t data; >> if (uap->com > 0xffffffff) { >> @@ -680,17 +681,18 @@ sys_ioctl(struct thread *td, struct ioct >> arg = (intptr_t)uap->data; >> data = (void *)&arg; >> size = 0; >> - } else >> - data = malloc((u_long)size, M_IOCTLOPS, M_WAITOK); >> + } else { >> + if (size <= sizeof(smalldata)) >> + data = smalldata; >> + else >> + data = malloc((u_long)size, M_IOCTLOPS, M_WAITOK); >> + } >> } else >> data = (void *)&uap->data; >> if (com & IOC_IN) { >> error = copyin(uap->data, data, (u_int)size); >> - if (error) { >> - if (size > 0) >> - free(data, M_IOCTLOPS); >> - return (error); >> - } >> + if (error != 0) >> + goto out; >> } else if (com & IOC_OUT) { >> /* >> * Zero the buffer so the user always >> @@ -704,7 +706,8 @@ sys_ioctl(struct thread *td, struct ioct >> if (error == 0 && (com & IOC_OUT)) >> error = copyout(data, uap->data, (u_int)size); >> - if (size > 0) >> +out: >> + if (size > 0 && data != (caddr_t)&smalldata) >> free(data, M_IOCTLOPS); >> return (error); >> } >> >> >> > > > >
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