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
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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