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From:   Daeho Jeong <daeho43@gmail.com>
Date:   Fri, 12 Jun 2020 07:49:12 +0900
Message-ID: <CACOAw_zKC24BhNOF2BpuRfuYzBEsis82MafU9HqXwLj2sZ3Azg@mail.gmail.com>
Subject: Re: [f2fs-dev] [PATCH v2] f2fs: add F2FS_IOC_SEC_TRIM_FILE ioctl
To:     Eric Biggers <ebiggers@kernel.org>
Cc:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com,
        Daeho Jeong <daehojeong@google.com>
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2020=EB=85=84 6=EC=9B=94 12=EC=9D=BC (=EA=B8=88) =EC=98=A4=EC=A0=84 1:27, E=
ric Biggers <ebiggers@kernel.org>=EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=B1:
>
> On Thu, Jun 11, 2020 at 12:16:52PM +0900, Daeho Jeong wrote:
> > +     for (index =3D pg_start; index < pg_end;) {
> > +             struct dnode_of_data dn;
> > +             unsigned int end_offset;
> > +
> > +             set_new_dnode(&dn, inode, NULL, NULL, 0);
> > +             ret =3D f2fs_get_dnode_of_data(&dn, index, LOOKUP_NODE);
> > +             if (ret)
> > +                     goto out;
> > +
> > +             end_offset =3D ADDRS_PER_PAGE(dn.node_page, inode);
> > +             if (pg_end < end_offset + index)
> > +                     end_offset =3D pg_end - index;
> > +
> > +             for (; dn.ofs_in_node < end_offset;
> > +                             dn.ofs_in_node++, index++) {
> > +                     struct block_device *cur_bdev;
> > +                     block_t blkaddr =3D f2fs_data_blkaddr(&dn);
> > +
> > +                     if (__is_valid_data_blkaddr(blkaddr)) {
> > +                             if (!f2fs_is_valid_blkaddr(F2FS_I_SB(inod=
e),
> > +                                     blkaddr, DATA_GENERIC_ENHANCE)) {
> > +                                     ret =3D -EFSCORRUPTED;
> > +                                     goto out;
> > +                             }
> > +                     } else
> > +                             continue;
> > +
> > +                     cur_bdev =3D f2fs_target_device(sbi, blkaddr, NUL=
L);
> > +                     if (f2fs_is_multi_device(sbi)) {
> > +                             int i =3D f2fs_target_device_index(sbi, b=
lkaddr);
> > +
> > +                             blkaddr -=3D FDEV(i).start_blk;
> > +                     }
> > +
> > +                     if (len) {
> > +                             if (prev_bdev =3D=3D cur_bdev &&
> > +                                     blkaddr =3D=3D prev_block + len) =
{
> > +                                     len++;
> > +                             } else {
> > +                                     ret =3D f2fs_secure_erase(prev_bd=
ev,
> > +                                                     prev_block, len, =
flags);
> > +                                     if (ret)
> > +                                             goto out;
> > +
> > +                                     len =3D 0;
> > +                             }
> > +                     }
> > +
> > +                     if (!len) {
> > +                             prev_bdev =3D cur_bdev;
> > +                             prev_block =3D blkaddr;
> > +                             len =3D 1;
> > +                     }
> > +             }
> > +
> > +             f2fs_put_dnode(&dn);
> > +     }
>
> This loop processes the entire file, which may be very large.  So it coul=
d take
> a very long time to execute.
>
> It should at least use the following to make the task killable and preemp=
tible:
>
>                 if (fatal_signal_pending(current)) {
>                         err =3D -EINTR;
>                         goto out;
>                 }
>                 cond_resched();
>

Good point!

> Also, perhaps this ioctl should be made incremental, i.e. take in an
> (offset, length) like pwrite()?
>
> - Eric

Discard and Zeroing will be treated in a unit of block, which is 4KB
in F2FS case.
Do you really need the (offset, length) option here even if the unit
is a 4KB block? I guess this option might make the user even
inconvenienced to use this ioctl, because they have to bear 4KB
alignment in mind.