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From:   Daeho Jeong <daeho43@gmail.com>
Date:   Thu, 29 Sep 2022 16:33:50 -0700
Message-ID: <CACOAw_wVU1gmH1gyWHYNqCpgy4KGKB+EZK6pbGL-h_1ToDV=vg@mail.gmail.com>
Subject: Re: [f2fs-dev] [PATCH v2] f2fs: introduce F2FS_IOC_START_ATOMIC_REPLACE
To:     Chao Yu <chao@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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On Thu, Sep 29, 2022 at 3:54 PM Chao Yu <chao@kernel.org> wrote:
>
> On 2022/9/30 0:13, Daeho Jeong wrote:
> > On Thu, Sep 29, 2022 at 12:36 AM Chao Yu <chao@kernel.org> wrote:
> >>
> >> On 2022/9/20 9:40, Daeho Jeong wrote:
> >>> From: Daeho Jeong <daehojeong@google.com>
> >>>
> >>> introduce a new ioctl to replace the whole content of a file atomically,
> >>> which means it induces truncate and content update at the same time.
> >>> We can start it with F2FS_IOC_START_ATOMIC_REPLACE and complete it with
> >>> F2FS_IOC_COMMIT_ATOMIC_WRITE. Or abort it with
> >>> F2FS_IOC_ABORT_ATOMIC_WRITE.
> >>>
> >>> Signed-off-by: Daeho Jeong <daehojeong@google.com>
> >>> ---
> >>> v2: add undefined ioctl number reported by <lkp@intel.com>
> >>> ---
> >>>    fs/f2fs/data.c            |  3 +++
> >>>    fs/f2fs/f2fs.h            |  1 +
> >>>    fs/f2fs/file.c            | 12 ++++++++++--
> >>>    fs/f2fs/segment.c         | 14 +++++++++++++-
> >>>    include/uapi/linux/f2fs.h |  1 +
> >>>    5 files changed, 28 insertions(+), 3 deletions(-)
> >>>
> >>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> >>> index 6cd29a575105..d3d32db3a25d 100644
> >>> --- a/fs/f2fs/data.c
> >>> +++ b/fs/f2fs/data.c
> >>> @@ -3438,6 +3438,9 @@ static int prepare_atomic_write_begin(struct f2fs_sb_info *sbi,
> >>>        else if (*blk_addr != NULL_ADDR)
> >>>                return 0;
> >>>
> >>> +     if (is_inode_flag_set(inode, FI_ATOMIC_REPLACE))
> >>> +             goto reserve_block;
> >>> +
> >>>        /* Look for the block in the original inode */
> >>>        err = __find_data_block(inode, index, &ori_blk_addr);
> >>>        if (err)
> >>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> >>> index 539da7f12cfc..2c49da12d6d8 100644
> >>> --- a/fs/f2fs/f2fs.h
> >>> +++ b/fs/f2fs/f2fs.h
> >>> @@ -764,6 +764,7 @@ enum {
> >>>        FI_COMPRESS_RELEASED,   /* compressed blocks were released */
> >>>        FI_ALIGNED_WRITE,       /* enable aligned write */
> >>>        FI_COW_FILE,            /* indicate COW file */
> >>> +     FI_ATOMIC_REPLACE,      /* indicate atomic replace */
> >>>        FI_MAX,                 /* max flag, never be used */
> >>>    };
> >>>
> >>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> >>> index 4f9b80c41b1e..4abd9d2a55b3 100644
> >>> --- a/fs/f2fs/file.c
> >>> +++ b/fs/f2fs/file.c
> >>> @@ -1982,7 +1982,7 @@ static int f2fs_ioc_getversion(struct file *filp, unsigned long arg)
> >>>        return put_user(inode->i_generation, (int __user *)arg);
> >>>    }
> >>>
> >>> -static int f2fs_ioc_start_atomic_write(struct file *filp)
> >>> +static int f2fs_ioc_start_atomic_write(struct file *filp, bool truncate)
> >>>    {
> >>>        struct inode *inode = file_inode(filp);
> >>>        struct user_namespace *mnt_userns = file_mnt_user_ns(filp);
> >>> @@ -2051,6 +2051,12 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
> >>>
> >>>        isize = i_size_read(inode);
> >>>        fi->original_i_size = isize;
> >>> +     if (truncate) {
> >>> +             set_inode_flag(inode, FI_ATOMIC_REPLACE);
> >>> +             truncate_inode_pages_final(inode->i_mapping);
> >>> +             f2fs_i_size_write(inode, 0);
> >>> +             isize = 0;
> >>> +     }
> >>
> >> Hi Daeho,
> >>
> >> isize should be updated after tagging inode as atomic_write one?
> >> otherwise f2fs_mark_inode_dirty_sync() may update isize to inode page,
> >> latter checkpoint may persist that change? IIUC...
> >>
> >> Thanks,
> >
> > Hi Chao,
> >
> > The first patch of this patchset prevents the inode page from being
> > updated as dirty for atomic file cases.
> > Is there any other chances for the inode page to be marked as dirty?
>
> I mean:
>
> Thread A                                Thread B
> - f2fs_ioc_start_atomic_write
>   - f2fs_i_size_write(inode, 0)
>    - f2fs_mark_inode_dirty_sync
>                                         - checkpoint
>                                          - persist inode with incorrect zero isize
>
>   - set_inode_flag(inode, FI_ATOMIC_FILE)
>
> Am I missing something?
>

So, f2fs_mark_inode_dirty_sync() will not work for atomic files
anymore, which means it doesn't make the inode dirty.
Plz, refer to the first patch of this patchset. Or I might be confused
with something. :(

@@ -30,6 +30,9 @@ void f2fs_mark_inode_dirty_sync(struct inode *inode,
bool sync)
        if (f2fs_inode_dirtied(inode, sync))
                return;

+       if (f2fs_is_atomic_file(inode))
+               return;
+
        mark_inode_dirty_sync(inode);
 }


> Thanks,
>
> >
> > Thanks,
> >
> >>
> >>>        f2fs_i_size_write(fi->cow_inode, isize);
> >>>
> >>>        spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
> >>> @@ -4080,7 +4086,9 @@ static long __f2fs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> >>>        case FS_IOC_GETVERSION:
> >>>                return f2fs_ioc_getversion(filp, arg);
> >>>        case F2FS_IOC_START_ATOMIC_WRITE:
> >>> -             return f2fs_ioc_start_atomic_write(filp);
> >>> +             return f2fs_ioc_start_atomic_write(filp, false);
> >>> +     case F2FS_IOC_START_ATOMIC_REPLACE:
> >>> +             return f2fs_ioc_start_atomic_write(filp, true);
> >>>        case F2FS_IOC_COMMIT_ATOMIC_WRITE:
> >>>                return f2fs_ioc_commit_atomic_write(filp);
> >>>        case F2FS_IOC_ABORT_ATOMIC_WRITE:
> >>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> >>> index 143b7ea0fb8e..c524538a9013 100644
> >>> --- a/fs/f2fs/segment.c
> >>> +++ b/fs/f2fs/segment.c
> >>> @@ -263,14 +263,26 @@ static void __complete_revoke_list(struct inode *inode, struct list_head *head,
> >>>                                        bool revoke)
> >>>    {
> >>>        struct revoke_entry *cur, *tmp;
> >>> +     pgoff_t start_index = 0;
> >>> +     bool truncate = is_inode_flag_set(inode, FI_ATOMIC_REPLACE);
> >>>
> >>>        list_for_each_entry_safe(cur, tmp, head, list) {
> >>> -             if (revoke)
> >>> +             if (revoke) {
> >>>                        __replace_atomic_write_block(inode, cur->index,
> >>>                                                cur->old_addr, NULL, true);
> >>> +             } else if (truncate) {
> >>> +                     f2fs_truncate_hole(inode, start_index, cur->index);
> >>> +                     start_index = cur->index + 1;
> >>> +             }
> >>> +
> >>>                list_del(&cur->list);
> >>>                kmem_cache_free(revoke_entry_slab, cur);
> >>>        }
> >>> +
> >>> +     if (!revoke && truncate) {
> >>> +             f2fs_do_truncate_blocks(inode, start_index * PAGE_SIZE, false);
> >>> +             clear_inode_flag(inode, FI_ATOMIC_REPLACE);
> >>> +     }
> >>>    }
> >>>
> >>>    static int __f2fs_commit_atomic_write(struct inode *inode)
> >>> diff --git a/include/uapi/linux/f2fs.h b/include/uapi/linux/f2fs.h
> >>> index 3121d127d5aa..955d440be104 100644
> >>> --- a/include/uapi/linux/f2fs.h
> >>> +++ b/include/uapi/linux/f2fs.h
> >>> @@ -42,6 +42,7 @@
> >>>                                                struct f2fs_comp_option)
> >>>    #define F2FS_IOC_DECOMPRESS_FILE    _IO(F2FS_IOCTL_MAGIC, 23)
> >>>    #define F2FS_IOC_COMPRESS_FILE              _IO(F2FS_IOCTL_MAGIC, 24)
> >>> +#define F2FS_IOC_START_ATOMIC_REPLACE        _IO(F2FS_IOCTL_MAGIC, 25)
> >>>
> >>>    /*
> >>>     * should be same as XFS_IOC_GOINGDOWN.