> > > > To prevent the file data from garbage collecting, the user needs to > > use pinfile ioctl and fallocate system call after creating the file. > > The sequence is like below. > > 1. create an empty file > > 2. pinfile > > 3. fallocate() > > Is that persistent? So the file will never be moved afterwards? > > Is there a place where this is (or should be) documented?
Yes, this is persistent. F2FS_IOC_SET_PIN_FILE ioctl is to prevent file data from moving and being garbage collected, and further update to the file will be handled in in-place update manner. I don't see any document on this, but you can find the below in Documentation/filesystems/f2fs.rst However, once F2FS receives ioctl(fd, F2FS_IOC_SET_PIN_FILE) in prior to fallocate(fd, DEFAULT_MODE), it allocates on-disk blocks addresses having zero or random data, which is useful to the below scenario where: 1. create(fd) 2. ioctl(fd, F2FS_IOC_SET_PIN_FILE) 3. fallocate(fd, 0, 0, size) 4. address = fibmap(fd, offset) 5. open(blkdev) 6. write(blkdev, address) > Right, the freezing check is actually still necessary. But getting write > access > to the mount is not necessary. I think you should use file_start_write() and > file_end_write(), like vfs_write() does. Yes, agreed. 2020년 6월 10일 (수) 오후 12:15, Eric Biggers <[email protected]>님이 작성: > > On Wed, Jun 10, 2020 at 11:05:46AM +0900, Daeho Jeong wrote: > > > > Added a new ioctl to send discard commands or/and zero out > > > > to whole data area of a regular file for security reason. > > > > > > With this ioctl available, what is the exact procedure to write and then > > > later > > > securely erase a file on f2fs? In particular, how can the user prevent > > > f2fs > > > from making multiple copies of file data blocks as part of garbage > > > collection? > > > > > > > To prevent the file data from garbage collecting, the user needs to > > use pinfile ioctl and fallocate system call after creating the file. > > The sequence is like below. > > 1. create an empty file > > 2. pinfile > > 3. fallocate() > > Is that persistent? So the file will never be moved afterwards? > > Is there a place where this is (or should be) documented? > > > > > + > > > > + if (f2fs_readonly(sbi->sb)) > > > > + return -EROFS; > > > > > > Isn't this redundant with mnt_want_write_file()? > > > > > > Also, shouldn't write access to the file be required, i.e. > > > (filp->f_mode & FMODE_WRITE)? Then the f2fs_readonly() and > > > mnt_want_write_file() checks would be unnecessary. > > > > > > > Using FMODE_WRITE is more proper for this case, since we're going to > > modify the data. But I think mnt_want_write_file() is still required > > to prevent the filesystem from freezing or something else. > > Right, the freezing check is actually still necessary. But getting write > access > to the mount is not necessary. I think you should use file_start_write() and > file_end_write(), like vfs_write() does. > > > > > > > > + > > > > + if (get_user(flags, (u32 __user *)arg)) > > > > + return -EFAULT; > > > > + if (!(flags & F2FS_TRIM_FILE_MASK)) > > > > + return -EINVAL; > > > > > > Need to reject unknown flags: > > > > > > if (flags & ~F2FS_TRIM_FILE_MASK) > > > return -EINVAL; > > > > I needed a different thing here. This was to check neither discard nor > > zeroing out are not here. But we still need to check unknown flags, > > too. > > The below might be better. > > if (!flags || flags & ~F2FS_TRIM_FILE_MASK) > > return -EINVAL; > > Sure, but please put parentheses around the second clause: > > if (flags == 0 || (flags & ~F2FS_TRIM_FILE_MASK)) > return -EINVAL; > > - Eric _______________________________________________ Linux-f2fs-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
