[Virtio-fs] [virtiofsd PATCH v4 3/4] virtiofsd: support per-file DAX negotiation in FUSE_INIT
Dr. David Alan Gilbert
dgilbert at redhat.com
Tue Aug 17 17:15:58 UTC 2021
* Jeffle Xu (jefflexu at linux.alibaba.com) wrote:
> In FUSE_INIT negotiating phase, server/client should advertise if it
> supports per-file DAX.
>
> Once advertising support for per-file DAX feature, virtiofsd should
> support storing FS_DAX_FL flag persistently passed by
> FS_IOC_SETFLAGS/FS_IOC_FSSETXATTR ioctl, and set FUSE_ATTR_DAX in
> FUSE_LOOKUP accordingly if the file is capable of per-file DAX.
>
> Currently only ext4/xfs since linux kernel v5.8 support storing
> FS_DAX_FL flag persistently, and thus advertise support for per-file
> DAX feature only when the backend fs type is ext4 and xfs.
I'm a little worried about the meaning of the flags we're storing and
the fact we're storing them in the normal host DAX flags.
Doesn't this mean that we're using a single host flag to mean:
a) It can be mapped as DAX on the host if it was a real DAX device
b) We can map it as DAX inside the guest with virtiofs?
what happens when we're using usernamespaces for the guest?
Dave
> Signed-off-by: Jeffle Xu <jefflexu at linux.alibaba.com>
> ---
> tools/virtiofsd/fuse_common.h | 5 +++++
> tools/virtiofsd/fuse_lowlevel.c | 6 ++++++
> tools/virtiofsd/passthrough_ll.c | 29 +++++++++++++++++++++++++++++
> 3 files changed, 40 insertions(+)
>
> diff --git a/tools/virtiofsd/fuse_common.h b/tools/virtiofsd/fuse_common.h
> index 8a75729be9..ee6fc64c23 100644
> --- a/tools/virtiofsd/fuse_common.h
> +++ b/tools/virtiofsd/fuse_common.h
> @@ -372,6 +372,11 @@ struct fuse_file_info {
> */
> #define FUSE_CAP_HANDLE_KILLPRIV_V2 (1 << 28)
>
> +/**
> + * Indicates support for per-file DAX.
> + */
> +#define FUSE_CAP_PERFILE_DAX (1 << 29)
> +
> /**
> * Ioctl flags
> *
> diff --git a/tools/virtiofsd/fuse_lowlevel.c b/tools/virtiofsd/fuse_lowlevel.c
> index 50fc5c8d5a..04a4f17423 100644
> --- a/tools/virtiofsd/fuse_lowlevel.c
> +++ b/tools/virtiofsd/fuse_lowlevel.c
> @@ -2065,6 +2065,9 @@ static void do_init(fuse_req_t req, fuse_ino_t nodeid,
> if (arg->flags & FUSE_HANDLE_KILLPRIV_V2) {
> se->conn.capable |= FUSE_CAP_HANDLE_KILLPRIV_V2;
> }
> + if (arg->flags & FUSE_PERFILE_DAX) {
> + se->conn.capable |= FUSE_CAP_PERFILE_DAX;
> + }
> #ifdef HAVE_SPLICE
> #ifdef HAVE_VMSPLICE
> se->conn.capable |= FUSE_CAP_SPLICE_WRITE | FUSE_CAP_SPLICE_MOVE;
> @@ -2180,6 +2183,9 @@ static void do_init(fuse_req_t req, fuse_ino_t nodeid,
> if (se->conn.want & FUSE_CAP_POSIX_ACL) {
> outarg.flags |= FUSE_POSIX_ACL;
> }
> + if (se->op.ioctl && (se->conn.want & FUSE_CAP_PERFILE_DAX)) {
> + outarg.flags |= FUSE_PERFILE_DAX;
> + }
> outarg.max_readahead = se->conn.max_readahead;
> outarg.max_write = se->conn.max_write;
> if (se->conn.max_background >= (1 << 16)) {
> diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
> index e170b17adb..5b6228210f 100644
> --- a/tools/virtiofsd/passthrough_ll.c
> +++ b/tools/virtiofsd/passthrough_ll.c
> @@ -53,8 +53,10 @@
> #include <sys/syscall.h>
> #include <sys/wait.h>
> #include <sys/xattr.h>
> +#include <sys/vfs.h>
> #include <syslog.h>
> #include <linux/fs.h>
> +#include <linux/magic.h>
>
> #include "qemu/cutils.h"
> #include "passthrough_helpers.h"
> @@ -136,6 +138,13 @@ enum {
> SANDBOX_CHROOT,
> };
>
> +/* capability of storing DAX flag persistently */
> +enum {
> + DAX_CAP_NONE, /* not supported */
> + DAX_CAP_FLAGS, /* stored in flags (FS_IOC_GETFLAGS/FS_IOC_SETFLAGS) */
> + DAX_CAP_XATTR, /* stored in xflags (FS_IOC_FSGETXATTR/FS_IOC_FSSETXATTR) */
> +};
> +
> typedef struct xattr_map_entry {
> char *key;
> char *prepend;
> @@ -161,6 +170,7 @@ struct lo_data {
> int readdirplus_clear;
> int allow_direct_io;
> int announce_submounts;
> + int perfile_dax_cap; /* capability of backend fs */
> bool use_statx;
> struct lo_inode root;
> GHashTable *inodes; /* protected by lo->mutex */
> @@ -703,6 +713,10 @@ static void lo_init(void *userdata, struct fuse_conn_info *conn)
> conn->want &= ~FUSE_CAP_HANDLE_KILLPRIV_V2;
> lo->killpriv_v2 = 0;
> }
> +
> + if (conn->capable & FUSE_CAP_PERFILE_DAX && lo->perfile_dax_cap ) {
> + conn->want |= FUSE_CAP_PERFILE_DAX;
> + }
> }
>
> static void lo_getattr(fuse_req_t req, fuse_ino_t ino,
> @@ -3800,6 +3814,7 @@ static void setup_root(struct lo_data *lo, struct lo_inode *root)
> int fd, res;
> struct stat stat;
> uint64_t mnt_id;
> + struct statfs statfs;
>
> fd = open("/", O_PATH);
> if (fd == -1) {
> @@ -3826,6 +3841,20 @@ static void setup_root(struct lo_data *lo, struct lo_inode *root)
> root->posix_locks = g_hash_table_new_full(
> g_direct_hash, g_direct_equal, NULL, posix_locks_value_destroy);
> }
> +
> + /*
> + * Currently only ext4/xfs since linux kernel v5.8 support storing
> + * FS_DAX_FL flag persistently. Ext4 accesses this flag through
> + * FS_IOC_G[S]ETFLAGS ioctl, while xfs accesses this flag through
> + * FS_IOC_FSG[S]ETXATTR ioctl.
> + */
> + res = fstatfs(fd, &statfs);
> + if (!res) {
> + if (statfs.f_type == EXT4_SUPER_MAGIC)
> + lo->perfile_dax_cap = DAX_CAP_FLAGS;
> + else if (statfs.f_type == XFS_SUPER_MAGIC)
> + lo->perfile_dax_cap = DAX_CAP_XATTR;
> + }
> }
>
> static guint lo_key_hash(gconstpointer key)
> --
> 2.27.0
>
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--
Dr. David Alan Gilbert / dgilbert at redhat.com / Manchester, UK
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