Date: Mon, 13 Aug 2001 18:01:00 +0200 From: "Sansonetti Laurent" <lorenzo@linuxbe.org> To: <freebsd-hackers@freebsd.org> Subject: allocating userland space to call open() on a kernel module Message-ID: <003101c12411$294adaa0$0201a8c0@teledisnet.be>
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Hello hackers,
I'm currently working on a kld syscall module which needs to read a config
file at startup (MOD_LOAD).
Following the advice of Eugene L. Vorokov, I tried to allocate some userland
space with mmap() to store a open_args struct, fill-it with copyout() /
subyte()... and call open with curproc on first argument.
open() returns 14, EFAULT = Path points outside the process's allocated
space (man 2 open). Allocating userland memory works (mmap() returns 0),
idem for munmap().
I need help.. it would be fine if you can help me. I'm new on modules
coding...
Here's the (bad) code, and thanks in advance (forgive-me for my horrible
english :p).
----------------------------------------------------------------------------
--------
static void *
malloc_space_userland(const int size)
{
struct mmap_args *ma;
int ret=0;
void *addr;
MALLOC(ma,struct mmap_args *,sizeof(struct mmap_args),M_RING1,M_NOWAIT);
ma->addr=0;
ma->len=size;
ma->prot=PROT_READ|PROT_WRITE;
ma->flags=MAP_ANON;
ma->fd=-1;
if (mmap(curproc,ma)!=0) ret=-1;
FREE(ma,M_RING1);
if ((addr=(void *)curproc->p_retval[0])==MAP_FAILED)
ret=-1;
return (!ret)?addr:NULL;
}
static int
free_space_userland(void *addr,const int size)
{
struct munmap_args *mua;
int ret=0;
MALLOC(mua,struct munmap_args *,sizeof(struct
munmap_args),M_RING1,M_NOWAIT);
mua->addr=addr;
mua->len=size;
if (munmap(curproc,mua)!=0) ret=-1;
FREE(mua,M_RING1);
return ret;
}
static int
read_config(void)
{
struct open_args *oa=NULL;
int filedes=0;
char *fn=CFG_FILENAME; /* #define CFG_FILENAME "/etc/foo.bar" */
if (!(oa=malloc_space_userland(sizeof(struct open_args)))) {
printf("Unable to allocate space\n"); return 0;
} /* WORKS */
copyout(fn,&oa->path,strlen(CFG_FILENAME)); /* returns 0. */
susword(&oa->flags,O_RDONLY); /* returns 0 */
/* here's the problem, open() returns 14 (EFAULT) ... */
if (!open(curproc,oa) && (filedes=(int)curproc->p_retval[0])>0) {
/* ... */
}
if (free_space_userland(oa,sizeof(struct open_args))==-1) {
printf("Unable to free space\n"); return 0;
} /* WORKS */
return (filedes<=0)?0:1;
}
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