[LTP] [PATCH] syscalls/ioctl_loop05: set loop blksize to bdev blksize

[Jan Stancek <jstancek@redhat.com>]

----- Original Message -----
> Hi Jan
> 
> 
> > Test is failing on s390, where default loop blksize is less than
> > backing dev's blksize (4096):
> >    tst_test.c:1247: INFO: Timeout per run is 0h 05m 00s
> >    tst_device.c:88: INFO: Found free device 0 '/dev/loop0'
> >    ioctl_loop05.c:116: INFO: /dev/loop0 default logical_block_size is 512
> >    ioctl_loop05.c:62: INFO: Without setting lo_offset or sizelimit
> >    ioctl_loop05.c:63: BROK: ioctl(3,LOOP_SET_DIRECT_IO,...) failed: EINVAL
> >    (22)
> > 
> After looking kernel code, I think removing BLKSSZGET ioctl is ok.
> Also since kernel commit 85560117d00 ("loop: change queue block size to
> match when using DIO"), it will change logic block size automaticly when
> fd is opened with O_DIRECT. Can we use it??ust a suggestion??

We could, but then we need to limit test to kernels 5.4 and later,
since we depend on behavior introduced by that commit.

> > Per kernel comment at __loop_update_dio(), direct io is supported
> > when "logical block size of loop is bigger than the backing device's".
> > 
> > Set loop blksize to one of backing device. Retry is there to avoid
> > EAGAIN warning "loop0 (test.img) has still dirty pages".
> > 
> > Signed-off-by: Jan Stancek <jstancek@redhat.com>
> > ---
> >   .../kernel/syscalls/ioctl/ioctl_loop05.c      | 21 +++++++++++++++++--
> >   1 file changed, 19 insertions(+), 2 deletions(-)
> > 
> > diff --git a/testcases/kernel/syscalls/ioctl/ioctl_loop05.c
> > b/testcases/kernel/syscalls/ioctl/ioctl_loop05.c
> > index 6c9ea2802981..a969978239a5 100644
> > --- a/testcases/kernel/syscalls/ioctl/ioctl_loop05.c
> > +++ b/testcases/kernel/syscalls/ioctl/ioctl_loop05.c
> > @@ -96,6 +96,9 @@ static void verify_ioctl_loop(void)
> >   
> >   static void setup(void)
> >   {
> > +	int fd;
> > +	struct stat buf;
> > +
> >   	if (tst_fs_type(".") == TST_TMPFS_MAGIC)
> >   		tst_brk(TCONF, "tmpfd doesn't support O_DIRECT flag");
> >   
> > @@ -105,6 +108,14 @@ static void setup(void)
> >   
> >   	sprintf(sys_loop_diopath, "/sys/block/loop%d/loop/dio", dev_num);
> >   	tst_fill_file("test.img", 0, 1024, 1024);
> > +
> > +	fd = SAFE_OPEN("test.img", O_RDONLY);
> > +	SAFE_FSTAT(fd, &buf);
> > +	SAFE_CLOSE(fd);
> > +
> > +	logical_block_size = buf.st_blksize;
> > +	tst_res(TINFO, "backing dev logical_block_size is %d",
> > logical_block_size);
> > +
> >   	tst_attach_device(dev_path, "test.img");
> >   	attach_flag = 1;
> >   	dev_fd = SAFE_OPEN(dev_path, O_RDWR);
> > @@ -112,8 +123,14 @@ static void setup(void)
> >   	if (ioctl(dev_fd, LOOP_SET_DIRECT_IO, 0) && errno == EINVAL)
> >   		tst_brk(TCONF, "LOOP_SET_DIRECT_IO is not supported");
> >   
> > -	SAFE_IOCTL(dev_fd, BLKSSZGET, &logical_block_size);
> > -	tst_res(TINFO, "%s default logical_block_size is %d", dev_path,
> > logical_block_size);
> > +	/*
> > +	 * from __loop_update_dio():
> > +	 *   We support direct I/O only if lo_offset is aligned with the
> > +	 *   logical I/O size of backing device, and the logical block
> > +	 *   size of loop is bigger than the backing device's and the loop
> > +	 *   needn't transform transfer.
> > +	 */
> > +	TST_RETRY_FUNC(ioctl(dev_fd, LOOP_SET_BLOCK_SIZE, logical_block_size),
> > TST_RETVAL_EQ0);
> LOOP_SET_DIRECT_IO was introduce since 4.10 and  LOOP_SET_BLOCK_SIZE
> ioctl was introduced since kernel 4.14, I guess we should add a check
> for LOOP_SET_BLOCK_SIZE in here.

Good point.