Due to the commit 65da4539803373ec4eec97ffc49ee90083e56efd, the O_DIRECT open flag of guest applications will be discarded by virtiofsd. While this behavior makes it consistent with the virtio-9p scheme when guest applications using direct I/O, we no longer have any chance to bypass the host page cache.
Therefore, we add a flag 'allow_directio' to lo_data. If '-o no_directio' option is added, or none of '-o no_directio' or '-o allow_directio' is added, the 'allow_directio' will be set to 0, and virtiofsd discards O_DIRECT as before. If '-o allow_directio' is added to the stariting command-line, 'allow_directio' will be set to 1, so that the O_DIRECT flags will be retained and host page cache can be bypassed. Signed-off-by: Jiachen Zhang <zhangjiachen.jay...@bytedance.com> --- tools/virtiofsd/helper.c | 4 ++++ tools/virtiofsd/passthrough_ll.c | 20 ++++++++++++++------ 2 files changed, 18 insertions(+), 6 deletions(-) diff --git a/tools/virtiofsd/helper.c b/tools/virtiofsd/helper.c index 3105b6c23a..534ff52c64 100644 --- a/tools/virtiofsd/helper.c +++ b/tools/virtiofsd/helper.c @@ -180,6 +180,10 @@ void fuse_cmdline_help(void) " (0 leaves rlimit unchanged)\n" " default: min(1000000, fs.file-max - 16384)\n" " if the current rlimit is lower\n" + " -o allow_directio|no_directio\n" + " retain/discard O_DIRECT flags passed down\n" + " to virtiofsd from guest applications.\n" + " default: no_directio\n" ); } diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c index 94e0de2d2b..1c5ea27821 100644 --- a/tools/virtiofsd/passthrough_ll.c +++ b/tools/virtiofsd/passthrough_ll.c @@ -151,6 +151,7 @@ struct lo_data { int timeout_set; int readdirplus_set; int readdirplus_clear; + int allow_directio; struct lo_inode root; GHashTable *inodes; /* protected by lo->mutex */ struct lo_map ino_map; /* protected by lo->mutex */ @@ -179,6 +180,8 @@ static const struct fuse_opt lo_opts[] = { { "cache=always", offsetof(struct lo_data, cache), CACHE_ALWAYS }, { "readdirplus", offsetof(struct lo_data, readdirplus_set), 1 }, { "no_readdirplus", offsetof(struct lo_data, readdirplus_clear), 1 }, + { "allow_directio", offsetof(struct lo_data, allow_directio), 1 }, + { "no_directio", offsetof(struct lo_data, allow_directio), 0 }, FUSE_OPT_END }; static bool use_syslog = false; @@ -1516,7 +1519,8 @@ static void lo_releasedir(fuse_req_t req, fuse_ino_t ino, fuse_reply_err(req, 0); } -static void update_open_flags(int writeback, struct fuse_file_info *fi) +static void update_open_flags(int writeback, int allow_directio, + struct fuse_file_info *fi) { /* * With writeback cache, kernel may send read requests even @@ -1541,10 +1545,13 @@ static void update_open_flags(int writeback, struct fuse_file_info *fi) /* * O_DIRECT in guest should not necessarily mean bypassing page - * cache on host as well. If somebody needs that behavior, it - * probably should be a configuration knob in daemon. + * cache on host as well. Therefore, we discard it by default + * ('-o no_directio'). If somebody needs that behavior, the + * '-o allow_directio' option should be set. */ - fi->flags &= ~O_DIRECT; + if (!allow_directio) { + fi->flags &= ~O_DIRECT; + } } static void lo_create(fuse_req_t req, fuse_ino_t parent, const char *name, @@ -1576,7 +1583,7 @@ static void lo_create(fuse_req_t req, fuse_ino_t parent, const char *name, goto out; } - update_open_flags(lo->writeback, fi); + update_open_flags(lo->writeback, lo->allow_directio, fi); fd = openat(parent_inode->fd, name, (fi->flags | O_CREAT) & ~O_NOFOLLOW, mode); @@ -1786,7 +1793,7 @@ static void lo_open(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi) fuse_log(FUSE_LOG_DEBUG, "lo_open(ino=%" PRIu64 ", flags=%d)\n", ino, fi->flags); - update_open_flags(lo->writeback, fi); + update_open_flags(lo->writeback, lo->allow_directio, fi); sprintf(buf, "%i", lo_fd(req, ino)); fd = openat(lo->proc_self_fd, buf, fi->flags & ~O_NOFOLLOW); @@ -2824,6 +2831,7 @@ int main(int argc, char *argv[]) .debug = 0, .writeback = 0, .posix_lock = 1, + .allow_directio = 0, .proc_self_fd = -1, }; struct lo_map_elem *root_elem; -- 2.11.0