Re: [LTP] [PATCH v2] statvfs01: Convert to new LTP API

Avinesh Kumar
2022-12-01T08:51:56Z

Hi Petr,

On Wednesday, November 30, 2022 3:20:37 PM IST Petr Vorel wrote:
> Hi all,
>
> ...
> > > +static struct tst_test test = {
> > > + .test_all = run,
> > > + .setup = setup,
> > > + .needs_root = 1,
> > > + .mount_device = 1,
> > > + .mntpoint = MNT_POINT,
> > > + .all_filesystems = 1,
> > > + .skip_filesystems = (const char *const[]) {
> > > + "vfat",
> > > + "exfat",
> > I was looking what's wrong with vfat and exfat.
> > statvfs.f_namemax returns 1530, which is obviously too long, thus valid_fname
> > obviously returns ENAMETOOLONG (36). Tested on 6.1.0-rc6-1.g4c01546-default.
> > I wonder why, isn't that a bug?
>
> To reply myself, both glibc and musl defines:
> statvfs->f_namemax = statfs->f_namelen;
>
> TL;DR: 6 * 255 = 1530 due names being in UTF-8:
>
> Therefore looking into kernel sources for statfs->f_namelen:
>
> include/linux/nls.h
> #define NLS_MAX_CHARSET_SIZE 6 /* for UTF-8 */
>
> === exfat ===
> exfat/exfat_raw.h
> #define EXFAT_MAX_FILE_LEN 255
>
> exfat/super.c
> static int exfat_statfs(struct dentry *dentry, struct kstatfs *buf)
> {
> ...
> /* Unicode utf16 255 characters */
> buf->f_namelen = EXFAT_MAX_FILE_LEN * NLS_MAX_CHARSET_SIZE;
>
> === vfat ===
> include/uapi/linux/msdos_fs.h
> #define FAT_LFN_LEN 255 /* maximum long name length */
>
> fat/inode.c
> static int fat_statfs(struct dentry *dentry, struct kstatfs *buf)
> {
> ...
> buf->f_namelen =
> (sbi->options.isvfat ? FAT_LFN_LEN : 12) * NLS_MAX_CHARSET_SIZE;
>
> => i.e. for vfat without long filename support it'd be 72.
>
> How about
> 1) don't skip exfat and vfat but just skip creating file with valid name? or
>
> 2) Add #define NLS_MAX_CHARSET_SIZE 6 and for vfat and exfat calculate
> length as: buf.f_namemax / NLS_MAX_CHARSET_SIZE - 1 ?
>
> Kind regards,
> Petr
>

Thank you for the review and research on vfat, exfat scenarios.
I have adopted the option 1 for now and sent a v3 of this patch.

Regards,
Avinesh