On Thu, Jun 08, 2017 at 03:20:57AM +0100, Al Viro wrote:
> On Wed, Jun 07, 2017 at 05:35:31PM -0700, Richard Narron wrote:
>
> > I am willing to test. I just turned on UFS_FS_WRITE for the very first time
> > running 4.12-rc4 and was able to copy a file of more than 2GB from one r/o
> > FreeBSD subpartition to another r/w FreeBSD subpartition.
> >
> > So it is already looking pretty good.
>
> The nasty cases are around short files, especially short files with holes.
> Linear writes as done by cp(1) will do nothing worse than bogus i_blocks
> (and possibly mangled counters in cylinder groups). Random write access
> to short files, OTOH, steps into a lot more codepaths...
>
> As for ->i_blocks, it triggers this:
>
> root@kvm1:/mnt# df .; mkdir a; rmdir a; df .
> Filesystem 1K-blocks Used Available Use% Mounted on
> /dev/loop0 507420 4504 462340 1% /mnt
> Filesystem 1K-blocks Used Available Use% Mounted on
> /dev/loop0 507420 4536 462308 1% /mnt
>
> Note the 32Kb (== one block on that ufs2) leaked here.
> Every iteration will leak another one. Similar for long
> symlinks...
Spot the bogosity:
static inline int _ubh_isblockset_(struct ufs_sb_private_info * uspi,
struct ufs_buffer_head * ubh, unsigned begin, unsigned block)
{
switch (uspi->s_fpb) {
case 8:
return (*ubh_get_addr (ubh, begin + block) == 0xff);
case 4:
return (*ubh_get_addr (ubh, begin + (block >> 1)) == (0x0f << ((block & 0x01) << 2)));
case 2:
return (*ubh_get_addr (ubh, begin + (block >> 2)) == (0x03 << ((block & 0x03) << 1)));
case 1:
return (*ubh_get_addr (ubh, begin + (block >> 3)) == (0x01 << (block & 0x07)));
}
return 0;
}
with
static inline void _ubh_setblock_(struct ufs_sb_private_info * uspi,
struct ufs_buffer_head * ubh, unsigned begin, unsigned block)
{
switch (uspi->s_fpb) {
case 8:
*ubh_get_addr(ubh, begin + block) = 0xff;
return;
case 4:
*ubh_get_addr(ubh, begin + (block >> 1)) |= (0x0f << ((block & 0x01) << 2));
return;
case 2:
*ubh_get_addr(ubh, begin + (block >> 2)) |= (0x03 << ((block & 0x03) << 1));
return;
case 1:
*ubh_get_addr(ubh, begin + (block >> 3)) |= (0x01 << ((block & 0x07)));
return;
}
}
The only saving grace is that UFS defaults to 8 fragments per block...
