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From be7f19b21c84004c5a0705f040b957fd1c609e2e Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Etienne=20Dubl=C3=A9?= <etienne.duble@imag.fr>
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Date: Sun, 20 Sep 2020 20:08:15 +0200
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Subject: [PATCH 3/4] Allow caching symlinks in kernel page cache. (#551)
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This commit defines a new capability called `FUSE_CAP_CACHE_SYMLINKS`.
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It is off by default but you can now enable it by setting this flag in
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in the `want` field of the `fuse_conn_info` structure.
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When enabled, the kernel will save symlinks in its page cache,
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by making use of the feature introduced in kernel 4.20:
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https://github.com/torvalds/linux/commit/5571f1e65486be025f73fa6aa30fb03725d362a2
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(cherry picked from commit ba3b225a126ebb3c6d4fe27c9f7c73aa4167001e)
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Signed-off-by: Pavel Reichl <preichl@redhat.com>
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---
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example/printcap.c | 2 ++
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include/fuse_common.h | 13 +++++++++++++
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lib/fuse_lowlevel.c | 4 ++++
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3 files changed, 19 insertions(+)
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diff --git a/example/printcap.c b/example/printcap.c
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index 77dea14..a66036f 100644
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--- a/example/printcap.c
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+++ b/example/printcap.c
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@@ -77,6 +77,8 @@ static void pc_init(void *userdata,
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printf("\tFUSE_CAP_PARALLEL_DIROPS\n");
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if(conn->capable & FUSE_CAP_POSIX_ACL)
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printf("\tFUSE_CAP_POSIX_ACL\n");
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+ if(conn->capable & FUSE_CAP_CACHE_SYMLINKS)
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+ printf("\tFUSE_CAP_CACHE_SYMLINKS\n");
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fuse_session_exit(se);
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}
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diff --git a/include/fuse_common.h b/include/fuse_common.h
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index 83c9dee..a5a0ea5 100644
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--- a/include/fuse_common.h
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+++ b/include/fuse_common.h
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@@ -316,6 +316,19 @@ struct fuse_loop_config {
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*/
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#define FUSE_CAP_HANDLE_KILLPRIV (1 << 20)
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+/**
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+ * Indicates that the kernel supports caching symlinks in its page cache.
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+ *
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+ * When this feature is enabled, symlink targets are saved in the page cache.
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+ * You can invalidate a cached link by calling:
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+ * `fuse_lowlevel_notify_inval_inode(se, ino, 0, 0);`
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+ *
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+ * This feature is disabled by default.
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+ * If the kernel supports it (>= 4.20), you can enable this feature by
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+ * setting this flag in the `want` field of the `fuse_conn_info` structure.
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+ */
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+#define FUSE_CAP_CACHE_SYMLINKS (1 << 23)
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+
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/**
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* Ioctl flags
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*
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diff --git a/lib/fuse_lowlevel.c b/lib/fuse_lowlevel.c
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index 60195e0..43f785f 100644
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--- a/lib/fuse_lowlevel.c
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+++ b/lib/fuse_lowlevel.c
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@@ -1882,6 +1882,8 @@ static void do_init(fuse_req_t req, fuse_ino_t nodeid, const void *inarg)
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se->conn.capable |= FUSE_CAP_POSIX_ACL;
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if (arg->flags & FUSE_HANDLE_KILLPRIV)
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se->conn.capable |= FUSE_CAP_HANDLE_KILLPRIV;
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+ if (arg->flags & FUSE_CACHE_SYMLINKS)
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+ se->conn.capable |= FUSE_CAP_CACHE_SYMLINKS;
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if (!(arg->flags & FUSE_MAX_PAGES)) {
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size_t max_bufsize =
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FUSE_DEFAULT_MAX_PAGES_PER_REQ * getpagesize()
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@@ -2002,6 +2004,8 @@ static void do_init(fuse_req_t req, fuse_ino_t nodeid, const void *inarg)
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outarg.flags |= FUSE_WRITEBACK_CACHE;
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if (se->conn.want & FUSE_CAP_POSIX_ACL)
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outarg.flags |= FUSE_POSIX_ACL;
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+ if (se->conn.want & FUSE_CAP_CACHE_SYMLINKS)
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+ outarg.flags |= FUSE_CACHE_SYMLINKS;
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outarg.max_readahead = se->conn.max_readahead;
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outarg.max_write = se->conn.max_write;
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if (se->conn.proto_minor >= 13) {
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--
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2.36.1
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