On Mon, 20 May 2024 at 01:23, Jiri Slaby <jirislaby@xxxxxxxxxx> wrote:
>
> So what about LEGACY_NO_MODE which would set "i_mode = 0" and mangle the
> WARN_ON appropriately. Like in the patch attached? It works (when
> applied together with the anon_inode name fix).
No, that's horrendous.
We actually have a much better place to handle this nasty thing:
pidfs_getattr() for the returned st_mode, and pidfs_dname() for the
name.
So how about just a patch like this? It doesn't do anything
*internally* to the inodes, but it fixes up what we expose to user
level to make it look like lsof expects.
Linus
fs/pidfs.c | 25 ++++++++++++++++++++++++-
1 file changed, 24 insertions(+), 1 deletion(-)
diff --git a/fs/pidfs.c b/fs/pidfs.c
index a63d5d24aa02..5231ddb27d25 100644
--- a/fs/pidfs.c
+++ b/fs/pidfs.c
@@ -169,6 +169,24 @@ static int pidfs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
return -EOPNOTSUPP;
}
+
+/*
+ * User space expects pidfs inodes to have no file type in st_mode.
+ *
+ * In particular, 'lsof' has this legacy logic:
+ *
+ * type = s->st_mode & S_IFMT;
+ * switch (type) {
+ * ...
+ * case 0:
+ * if (!strcmp(p, "anon_inode"))
+ * Lf->ntype = Ntype = N_ANON_INODE;
+ *
+ * to detect our old anon_inode logic.
+ *
+ * Rather than mess with our internal sane inode data, just fix it
+ * up here in getattr() by masking off the format bits.
+ */
static int pidfs_getattr(struct mnt_idmap *idmap, const struct path *path,
struct kstat *stat, u32 request_mask,
unsigned int query_flags)
@@ -176,6 +194,7 @@ static int pidfs_getattr(struct mnt_idmap *idmap, const struct path *path,
struct inode *inode = d_inode(path->dentry);
generic_fillattr(&nop_mnt_idmap, request_mask, inode, stat);
+ stat->mode &= ~S_IFMT;
return 0;
}
@@ -199,12 +218,16 @@ static const struct super_operations pidfs_sops = {
.statfs = simple_statfs,
};
+/*
+ * 'lsof' has knowledge of out historical anon_inode use, and expects
+ * the pidfs dentry name to start with 'anon_inode'.
+ */
static char *pidfs_dname(struct dentry *dentry, char *buffer, int buflen)
{
struct inode *inode = d_inode(dentry);
struct pid *pid = inode->i_private;
- return dynamic_dname(buffer, buflen, "pidfd:[%llu]", pid->ino);
+ return dynamic_dname(buffer, buflen, "anon_inode:[pidfd-%llu]", pid->ino);
}
static const struct dentry_operations pidfs_dentry_operations = {
