io_uring always punts opens to async context, since there's no control
over whether the lookup blocks or not. Add LOOKUP_NONBLOCK to support
just doing the fast RCU based lookups, which we know will not block. If
we can do a cached path resolution of the filename, then we don't have
to always punt lookups for a worker.
During path resolution, we always do LOOKUP_RCU first. If that fails and
we terminate LOOKUP_RCU, then fail a LOOKUP_NONBLOCK attempt as well.
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
fs/namei.c | 9 +++++++++
include/linux/namei.h | 1 +
2 files changed, 10 insertions(+)
diff --git a/fs/namei.c b/fs/namei.c
index 7eb7830da298..07a1aa874f65 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -686,6 +686,8 @@ static bool try_to_unlazy(struct nameidata *nd)
BUG_ON(!(nd->flags & LOOKUP_RCU));
nd->flags &= ~LOOKUP_RCU;
+ if (nd->flags & LOOKUP_NONBLOCK)
+ goto out1;
if (unlikely(!legitimize_links(nd)))
goto out1;
if (unlikely(!legitimize_path(nd, &nd->path, nd->seq)))
@@ -722,6 +724,8 @@ static int unlazy_child(struct nameidata *nd, struct dentry *dentry, unsigned se
BUG_ON(!(nd->flags & LOOKUP_RCU));
nd->flags &= ~LOOKUP_RCU;
+ if (nd->flags & LOOKUP_NONBLOCK)
+ goto out2;
if (unlikely(!legitimize_links(nd)))
goto out2;
if (unlikely(!legitimize_mnt(nd->path.mnt, nd->m_seq)))
@@ -792,6 +796,7 @@ static int complete_walk(struct nameidata *nd)
*/
if (!(nd->flags & (LOOKUP_ROOT | LOOKUP_IS_SCOPED)))
nd->root.mnt = NULL;
+ nd->flags &= ~LOOKUP_NONBLOCK;
if (!try_to_unlazy(nd))
return -ECHILD;
}
@@ -2202,6 +2207,10 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
int error;
const char *s = nd->name->name;
+ /* LOOKUP_NONBLOCK requires RCU, ask caller to retry */
+ if ((flags & (LOOKUP_RCU | LOOKUP_NONBLOCK)) == LOOKUP_NONBLOCK)
+ return ERR_PTR(-EAGAIN);
+
if (!*s)
flags &= ~LOOKUP_RCU;
if (flags & LOOKUP_RCU)
diff --git a/include/linux/namei.h b/include/linux/namei.h
index a4bb992623c4..c36c4e0805fc 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -46,6 +46,7 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT};
#define LOOKUP_NO_XDEV 0x040000 /* No mountpoint crossing. */
#define LOOKUP_BENEATH 0x080000 /* No escaping from starting point. */
#define LOOKUP_IN_ROOT 0x100000 /* Treat dirfd as fs root. */
+#define LOOKUP_NONBLOCK 0x200000 /* don't block for lookup */
/* LOOKUP_* flags which do scope-related checks based on the dirfd. */
#define LOOKUP_IS_SCOPED (LOOKUP_BENEATH | LOOKUP_IN_ROOT)
--
2.29.2
