From: Bernd Schubert <bschubert@ddn.com>
Date: Mon, 4 Dec 2023 14:58:45 +0000 (+0100)
Subject: Add FUSE_CAP_DIRECT_IO_ALLOW_MMAP and use in passthrough_hp
X-Git-Tag: fuse-3.17.1-rc0~158
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=22741f5582ea003c3518aff76e8df6561403f88b;p=qemu-gpiodev%2Flibfuse.git

Add FUSE_CAP_DIRECT_IO_ALLOW_MMAP and use in passthrough_hp

This is not called FUSE_CAP_DIRECT_IO_RELAX, as the kernel flag
FUSE_DIRECT_IO_RELAX is supposed to be renamed to
FUSE_DIRECT_IO_ALLOW_MMAP. The corresponding kernel patches just
did not land yet.
---

diff --git a/example/passthrough_hp.cc b/example/passthrough_hp.cc
index 96201d6..66fe6f8 100644
--- a/example/passthrough_hp.cc
+++ b/example/passthrough_hp.cc
@@ -212,6 +212,10 @@ static void sfs_init(void *userdata, fuse_conn_info *conn) {
         if (conn->capable & FUSE_CAP_SPLICE_READ)
             conn->want |= FUSE_CAP_SPLICE_READ;
     }
+
+    /* This is a local file system - no network coherency needed */
+    if (conn->capable & FUSE_CAP_DIRECT_IO_ALLOW_MMAP)
+        conn->want |= FUSE_CAP_DIRECT_IO_ALLOW_MMAP;
 }
 
 
diff --git a/include/fuse_common.h b/include/fuse_common.h
index 3ff14ec..a804134 100644
--- a/include/fuse_common.h
+++ b/include/fuse_common.h
@@ -440,6 +440,15 @@ struct fuse_loop_config_v1 {
  */
 #define FUSE_CAP_SETXATTR_EXT     (1 << 27)
 
+/**
+ * Files opened with FUSE_DIRECT_IO do not support MAP_SHARED mmap. This restriction
+ * is relaxed through FUSE_CAP_DIRECT_IO_RELAX (kernel flag: FUSE_DIRECT_IO_RELAX).
+ * MAP_SHARED is disabled by default for FUSE_DIRECT_IO, as this flag can be used to
+ * ensure coherency between mount points (or network clients) and with kernel page
+ * cache as enforced by mmap that cannot be guaranteed anymore.
+ */
+#define FUSE_CAP_DIRECT_IO_ALLOW_MMAP  (1 << 27)
+
 /**
  * Ioctl flags
  *
diff --git a/lib/fuse_lowlevel.c b/lib/fuse_lowlevel.c
index ea98536..41e626b 100644
--- a/lib/fuse_lowlevel.c
+++ b/lib/fuse_lowlevel.c
@@ -2019,6 +2019,8 @@ void do_init(fuse_req_t req, fuse_ino_t nodeid, const void *inarg)
 				bufsize = max_bufsize;
 			}
 		}
+		if (inargflags & FUSE_DIRECT_IO_ALLOW_MMAP)
+			se->conn.capable |= FUSE_CAP_DIRECT_IO_ALLOW_MMAP;
 		if (arg->minor >= 38)
 			se->conn.capable |= FUSE_CAP_EXPIRE_ONLY;
 	} else {
@@ -2151,6 +2153,8 @@ void do_init(fuse_req_t req, fuse_ino_t nodeid, const void *inarg)
 		outargflags |= FUSE_EXPLICIT_INVAL_DATA;
 	if (se->conn.want & FUSE_CAP_SETXATTR_EXT)
 		outargflags |= FUSE_SETXATTR_EXT;
+	if (se->conn.want & FUSE_CAP_DIRECT_IO_ALLOW_MMAP)
+		outargflags |= FUSE_DIRECT_IO_ALLOW_MMAP;
 
 	if (inargflags & FUSE_INIT_EXT) {
 		outargflags |= FUSE_INIT_EXT;