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

[Petr Vorel <pvorel@suse.cz>]

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

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