On Tue, Aug 27, 2024 at 10:32:38AM +0800, Hongbo Li wrote: > > > On 2024/8/27 10:13, Darrick J. Wong wrote: > > On Tue, Aug 27, 2024 at 01:41:08AM +0000, Hongbo Li wrote: > > > Many mainstream file systems already support the GETVERSION ioctl, > > > and their implementations are completely the same, essentially > > > just obtain the value of i_generation. We think this ioctl can be > > > implemented at the VFS layer, so the file systems do not need to > > > implement it individually. > > > > What if a filesystem never touches i_generation? Is it ok to advertise > > a generation number of zero when that's really meaningless? Or should > > we gate the generic ioctl on (say) whether or not the fs implements file > > handles and/or supports nfs? > > This ioctl mainly returns the i_generation, and whether it has meaning is up > to the specific file system. Some tools will invoke IOC_GETVERSION, such as > `lsattr -v`(but if it's lattr, it won't), but users may not necessarily > actually use this value. That's not how that works. If the kernel starts exporting a datum, people will start using it, and then the expectation that it will *continue* to work becomes ingrained in the userspace ABI forever. Be careful about establishing new behaviors for vfat. --D > Thanks, > Hongbo > > > > > --D > > > > > Signed-off-by: Hongbo Li <lihongbo22@xxxxxxxxxx> > > > --- > > > fs/ioctl.c | 6 ++++++ > > > 1 file changed, 6 insertions(+) > > > > > > diff --git a/fs/ioctl.c b/fs/ioctl.c > > > index 64776891120c..dff887ec52c4 100644 > > > --- a/fs/ioctl.c > > > +++ b/fs/ioctl.c > > > @@ -878,6 +878,9 @@ static int do_vfs_ioctl(struct file *filp, unsigned int fd, > > > case FS_IOC_GETFSUUID: > > > return ioctl_getfsuuid(filp, argp); > > > + case FS_IOC_GETVERSION: > > > + return put_user(inode->i_generation, (int __user *)argp); > > > + > > > case FS_IOC_GETFSSYSFSPATH: > > > return ioctl_get_fs_sysfs_path(filp, argp); > > > @@ -992,6 +995,9 @@ COMPAT_SYSCALL_DEFINE3(ioctl, unsigned int, fd, unsigned int, cmd, > > > cmd = (cmd == FS_IOC32_GETFLAGS) ? > > > FS_IOC_GETFLAGS : FS_IOC_SETFLAGS; > > > fallthrough; > > > + case FS_IOC32_GETVERSION: > > > + cmd = FS_IOC_GETVERSION; > > > + fallthrough; > > > /* > > > * everything else in do_vfs_ioctl() takes either a compatible > > > * pointer argument or no argument -- call it with a modified > > > -- > > > 2.34.1 > > > > > > > > >
