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authorJens Axboe <axboe@kernel.dk>2020-12-17 09:19:09 -0700
committerAl Viro <viro@zeniv.linux.org.uk>2021-01-04 11:42:21 -0500
commit6c6ec2b0a3e0381d886d531bd1471dfdb1509237 (patch)
tree87edec0a250e14b3929f970917f34547a316c850
parentae66db45fd309fd1c6d4e846dfc8414dfec7d6ad (diff)
fs: add support for LOOKUP_CACHED
io_uring always punts opens to async context, since there's no control over whether the lookup blocks or not. Add LOOKUP_CACHED 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_CACHED attempt as well. Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
-rw-r--r--fs/namei.c9
-rw-r--r--include/linux/namei.h1
2 files changed, 10 insertions, 0 deletions
diff --git a/fs/namei.c b/fs/namei.c
index 2ee219497460..4cae88733a5c 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_CACHED)
+ goto out1;
if (unlikely(!legitimize_links(nd)))
goto out1;
if (unlikely(!legitimize_path(nd, &nd->path, nd->seq)))
@@ -722,6 +724,8 @@ static bool try_to_unlazy_next(struct nameidata *nd, struct dentry *dentry, unsi
BUG_ON(!(nd->flags & LOOKUP_RCU));
nd->flags &= ~LOOKUP_RCU;
+ if (nd->flags & LOOKUP_CACHED)
+ 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_CACHED;
if (!try_to_unlazy(nd))
return -ECHILD;
}
@@ -2204,6 +2209,10 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
int error;
const char *s = nd->name->name;
+ /* LOOKUP_CACHED requires RCU, ask caller to retry */
+ if ((flags & (LOOKUP_RCU | LOOKUP_CACHED)) == LOOKUP_CACHED)
+ 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..b9605b2b46e7 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_CACHED 0x200000 /* Only do cached lookup */
/* LOOKUP_* flags which do scope-related checks based on the dirfd. */
#define LOOKUP_IS_SCOPED (LOOKUP_BENEATH | LOOKUP_IN_ROOT)