>| How can I obtains an buffer alignement from a "user program" ? > >I actually left that as an exercise (after I did it at home >last night). Did you read the hint (below)?
Well ... either with malloc() and alignement or posix_memalign(), read() still failed! My read buffer is in user space, so it's copy to kernel space. Inside the read() call, it's the kernel buffer which must be aligned?
>
>| >In fs/buffer.c, it wants the buffer & the length (size) to be aligned:
>| >
>| >function: brw_kiovec()
>| >
>| > /*
>| > * First, do some alignment and validity checks
>| > */
>| > for (i = 0; i < nr; i++) {
>| > iobuf = iovec[i];
>| > if ((iobuf->offset & (size-1)) ||
>| > (iobuf->length & (size-1)))
>| > return -EINVAL;
>| > if (!iobuf->nr_pages)
>| > panic("brw_kiovec: iobuf not initialised");
>| > }
>| >
>| >so in your program, malloc() the buf [pointer] (larger than needed)
>| >and then align it to a page boundary and pass that aligned pointer
>| >to read().
>| >
/* --- start code --- */
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>#define O_BINARY 0
int main(int argc,char *argv[])
{
struct stat sbuf;
char * buf;
int openFlags;
int fd;
int nb;
off_t size;
blksize_t blksize;
off_t offset;if (argc!=2){
printf("Missing file name\n");
exit(2);
}
printf("[%s]\n",argv[1]);
openFlags = O_RDWR|O_BINARY|O_NOCTTY;
openFlags |= O_DIRECT; /* Not POSIX */
fd = open(argv[1],openFlags,0666);
if (fd==-1){
printf("open failed [%s] %#o %#o errno %d\n",argv[1],openFlags,0666,errno);
exit(1);
}
if (fstat(fd,&sbuf)<0){
printf("fstat failed\n");
exit(1);
}
blksize = sbuf.st_blksize;
size = sbuf.st_size;
nb = posix_memalign((void **)&buf,blksize,size);
if (nb!=0){
printf("posix_memalign blksize %lu size %lu failed %d\n",blksize,size,nb);
exit(3);
}
#if 0
free(buf);
buf = malloc(2*blksize);
#endif
printf("direct: buf %p buf & (blksize-1) %lu\n",buf,(unsigned long)buf & (unsigned long)(blksize-1));
for (offset=0;offset<blksize;offset++){
if (!((unsigned long)(buf+offset) & (unsigned long)(blksize-1))){
printf("offset: buf %p buf & (blksize-1) %lu offset %lu\n",buf+offset,(unsigned long)(buf+offset) & (unsigned long)(blksize-1),offset);
break;
}
}
printf("align: buf %p buf & (blksize-1) %lu\n",buf+offset,(unsigned long)(buf+offset) & (unsigned long)(blksize-1));
nb = read(fd,buf+offset,blksize);
if (nb != blksize){
printf("read failed fd %d buf %p buf & (blksize-1) %lu blksize %lu size %lu nb %d errno %d\n",
fd,buf+offset,(unsigned long)(buf+offset) & (unsigned long)(blksize-1),
(unsigned long)blksize,size,nb,errno);
exit(1);
}
if (close(fd)){
printf("close failed\n");
exit(1);
}
free(buf);
return 0;
}
/* --- end code --- */
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