Messages in this thread | | | Date | Wed, 13 Apr 2005 15:15:47 +0200 | From | Yves Crespin <> | Subject | Re: read failed EINVAL with O_DIRECT flag |
| |
>| 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 --- */
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |