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

diff --git a/ChangeLog.rst b/ChangeLog.rst
index d176dfa6368fa5d5695c111b1a08288ae3cb1d8c..4cb14788d8ae3d181efd49b5db6e02767b32a489 100644 (file)
--- a/ChangeLog.rst
+++ b/ChangeLog.rst
@@ -1,7 +1,7 @@
 Unreleased Changes
 ==================
 
-* (none so far)
+* Add FUSE_CAP_CACHE_SYMLINKS: allow caching symlinks in kernel page cache.
 
 libfuse 3.9.4 (2020-08-09)
 ==========================

diff --git a/example/printcap.c b/example/printcap.c
index e0eb6b614dfa1f8e5621589159a669a5d5e519b9..bf058f5dd34f947c75583d0ec5e05f6668de4ed8 100644 (file)
--- a/example/printcap.c
+++ b/example/printcap.c
@@ -77,6 +77,8 @@ static void pc_init(void *userdata,
                        printf("\tFUSE_CAP_PARALLEL_DIROPS\n");
        if(conn->capable & FUSE_CAP_POSIX_ACL)
                        printf("\tFUSE_CAP_POSIX_ACL\n");
+       if(conn->capable & FUSE_CAP_CACHE_SYMLINKS)
+                       printf("\tFUSE_CAP_CACHE_SYMLINKS\n");
        if(conn->capable & FUSE_CAP_NO_OPENDIR_SUPPORT)
                        printf("\tFUSE_CAP_NO_OPENDIR_SUPPORT\n");
        if(conn->capable & FUSE_CAP_EXPLICIT_INVAL_DATA)

diff --git a/include/fuse_common.h b/include/fuse_common.h
index 39937d3506531c44d607d3f677a96ee501873c1c..f5bfb6a9f6c60c66d9f673445658ce163d9c3f3b 100644 (file)
--- a/include/fuse_common.h
+++ b/include/fuse_common.h
@@ -346,6 +346,19 @@ 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

diff --git a/lib/fuse_lowlevel.c b/lib/fuse_lowlevel.c
index 21379c10e568836344918d8f398f7877b9a15369..83510b3cdbb4c7b9dfacadc70aa8cc4b21613d3a 100644 (file)
--- a/lib/fuse_lowlevel.c
+++ b/lib/fuse_lowlevel.c
@@ -1963,6 +1963,8 @@ void do_init(fuse_req_t req, fuse_ino_t nodeid, const void *inarg)
                        se->conn.capable |= FUSE_CAP_POSIX_ACL;
                if (arg->flags & FUSE_HANDLE_KILLPRIV)
                        se->conn.capable |= FUSE_CAP_HANDLE_KILLPRIV;
+               if (arg->flags & FUSE_CACHE_SYMLINKS)
+                       se->conn.capable |= FUSE_CAP_CACHE_SYMLINKS;
                if (arg->flags & FUSE_NO_OPENDIR_SUPPORT)
                        se->conn.capable |= FUSE_CAP_NO_OPENDIR_SUPPORT;
                if (arg->flags & FUSE_EXPLICIT_INVAL_DATA)
@@ -2087,6 +2089,8 @@ void do_init(fuse_req_t req, fuse_ino_t nodeid, const void *inarg)
                outarg.flags |= FUSE_WRITEBACK_CACHE;
        if (se->conn.want & FUSE_CAP_POSIX_ACL)
                outarg.flags |= FUSE_POSIX_ACL;
+       if (se->conn.want & FUSE_CAP_CACHE_SYMLINKS)
+               outarg.flags |= FUSE_CACHE_SYMLINKS;
        if (se->conn.want & FUSE_CAP_EXPLICIT_INVAL_DATA)
                outarg.flags |= FUSE_EXPLICIT_INVAL_DATA;
        outarg.max_readahead = se->conn.max_readahead;