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    Subject[PATCH v7] f2fs: introduce F2FS_IOC_START_ATOMIC_REPLACE
    Date
    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>
    ---
    v7: changed where to clear FI_ATOMIC_REPLACE
    fixed tentative race condition in f2fs_ioc_start_atomic_write()
    v3: move i_size change after setting atomic write flag
    v2: add undefined ioctl number reported by <lkp@intel.com>
    ---
    fs/f2fs/data.c | 3 +++
    fs/f2fs/f2fs.h | 1 +
    fs/f2fs/file.c | 21 +++++++++++++++------
    fs/f2fs/segment.c | 13 ++++++++++++-
    include/uapi/linux/f2fs.h | 1 +
    5 files changed, 32 insertions(+), 7 deletions(-)

    diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
    index 5f895ddcd64a..bce4dcc3ad78 100644
    --- a/fs/f2fs/data.c
    +++ b/fs/f2fs/data.c
    @@ -3457,6 +3457,9 @@ 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 e29f9adf60ca..d513ecd17550 100644
    --- a/fs/f2fs/f2fs.h
    +++ b/fs/f2fs/f2fs.h
    @@ -765,6 +765,7 @@ enum {
    FI_ALIGNED_WRITE, /* enable aligned write */
    FI_COW_FILE, /* indicate COW file */
    FI_ATOMIC_COMMITTED, /* indicate atomic commit completed except disk sync */
    + 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 7ce629c95f4a..f9a04f6d76cb 100644
    --- a/fs/f2fs/file.c
    +++ b/fs/f2fs/file.c
    @@ -1984,7 +1984,7 @@ 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);
    @@ -2053,15 +2053,22 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)

    f2fs_write_inode(inode, NULL);

    - isize = i_size_read(inode);
    - fi->original_i_size = isize;
    - f2fs_i_size_write(fi->cow_inode, isize);
    -
    stat_inc_atomic_inode(inode);

    set_inode_flag(inode, FI_ATOMIC_FILE);
    set_inode_flag(fi->cow_inode, FI_COW_FILE);
    clear_inode_flag(fi->cow_inode, FI_INLINE_DATA);
    +
    + 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;
    + }
    + f2fs_i_size_write(fi->cow_inode, isize);
    +
    f2fs_up_write(&fi->i_gc_rwsem[WRITE]);

    f2fs_update_time(sbi, REQ_TIME);
    @@ -4089,7 +4096,9 @@ 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 9cbf88092c78..f2930fffbc7d 100644
    --- a/fs/f2fs/segment.c
    +++ b/fs/f2fs/segment.c
    @@ -197,6 +197,7 @@ void f2fs_abort_atomic_write(struct inode *inode, bool clean)
    fi->cow_inode = NULL;
    release_atomic_write_cnt(inode);
    clear_inode_flag(inode, FI_ATOMIC_COMMITTED);
    + clear_inode_flag(inode, FI_ATOMIC_REPLACE);
    clear_inode_flag(inode, FI_ATOMIC_FILE);
    stat_dec_atomic_inode(inode);

    @@ -261,14 +262,24 @@ 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);
    }

    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.
    --
    2.38.1.431.g37b22c650d-goog
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