On Tue, Dec 10, 2024 at 02:45:23AM +0000, Al Viro wrote:
> On Mon, Dec 09, 2024 at 11:12:37PM +0000, Al Viro wrote:
> >
> > Actually, grepping for DNAME_INLINE_LEN brings some interesting hits:
> > drivers/net/ieee802154/adf7242.c:1165: char debugfs_dir_name[DNAME_INLINE_LEN + 1];
> > cargo-culted, AFAICS; would be better off with a constant of their own.
> >
> > fs/ext4/fast_commit.c:326: fc_dentry->fcd_name.len > DNAME_INLINE_LEN)
> > fs/ext4/fast_commit.c:452: if (dentry->d_name.len > DNAME_INLINE_LEN) {
> > fs/ext4/fast_commit.c:1332: fc_dentry->fcd_name.len > DNAME_INLINE_LEN)
> > fs/ext4/fast_commit.h:113: unsigned char fcd_iname[DNAME_INLINE_LEN]; /* Dirent name string */
> > Looks like that might want struct name_snapshot, along with
> > {take,release}_dentry_name_snapshot().
>
> See viro/vfs.git#work.dcache. I've thrown ext4/fast_commit conversion
> into the end of that pile. NOTE: that stuff obviously needs profiling.
> It does survive light testing (boot/ltp/xfstests), but review and more
> testing (including serious profiling) is obviously needed.
>
> Patches in followups...
More fun with ->d_name, ->d_iname and friends:
87ce955b24c9 "io_uring: add ->show_fdinfo() for the io_uring file descriptor"
is playing silly buggers with ->d_iname for some reason. This
seq_printf(m, "UserFiles:\t%u\n", ctx->file_table.data.nr);
for (i = 0; has_lock && i < ctx->file_table.data.nr; i++) {
struct file *f = NULL;
if (ctx->file_table.data.nodes[i])
f = io_slot_file(ctx->file_table.data.nodes[i]);
if (f)
seq_printf(m, "%5u: %s\n", i, file_dentry(f)->d_iname);
else
seq_printf(m, "%5u: <none>\n", i);
}
produces user-visible data. For each slot in io_uring file table you
show either that it's empty (fine) or, for files with short names, the
last component of the name (no quoting, etc. - just a string as-is) or
the last short name that dentry used to have.
And that's a user-visible ABI. What the hell?
NOTE: file here is may be anything whatsoever. It may be a pipe,
an arbitrary file in tmpfs, a socket, etc.
How hard an ABI it is? If it's really used by random userland code
(admin tools, etc.), we have a problem. If that thing is cast in
stone, we'll have to emulate the current behaviour of that code,
no matter what. I really hope it can be replaced with something
saner, though.
Incidentally, call your file "<none>"; is the current behaviour
the right thing to do?
What behaviour _is_ actually wanted? Jens, Jann?
