Allow caching symlinks in kernel page cache. (#551)

This commit defines a new capability called `FUSE_CAP_CACHE_SYMLINKS`.
It is off by default but you can now enable it by setting this flag in
in the `want` field of the `fuse_conn_info` structure.

When enabled, the kernel will save symlinks in its page cache,
by making use of the feature introduced in kernel 4.20:
https://github.com/torvalds/linux/commit/5571f1e65486be025f73fa6aa30fb03725d362a2

1 files changed, 13 insertions, 0 deletions

diff --git a/include/fuse_common.h b/include/fuse_common.h
index 39937d3..f5bfb6a 100644
--- a/include/fuse_common.h
+++ b/include/fuse_common.h
@@ -347,6 +347,19 @@ struct fuse_loop_config {
 #define FUSE_CAP_HANDLE_KILLPRIV         (1 << 20)
 
 /**
+ * Indicates that the kernel supports caching symlinks in its page cache.
+ *
+ * When this feature is enabled, symlink targets are saved in the page cache.
+ * You can invalidate a cached link by calling:
+ * `fuse_lowlevel_notify_inval_inode(se, ino, 0, 0);`
+ *
+ * This feature is disabled by default.
+ * If the kernel supports it (>= 4.20), you can enable this feature by
+ * setting this flag in the `want` field of the `fuse_conn_info` structure.
+ */
+#define FUSE_CAP_CACHE_SYMLINKS        (1 << 23)
+
+/**
  * Indicates support for zero-message opendirs. If this flag is set in
  * the `capable` field of the `fuse_conn_info` structure, then the filesystem
  * may return `ENOSYS` from the opendir() handler to indicate success. Further