| Message ID | 20210817022347.18098-5-jefflexu@linux.alibaba.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | virtiofsd: support per-file DAX | expand |
* Jeffle Xu (jefflexu@linux.alibaba.com) wrote: > For passthrough, when the corresponding virtiofs in guest is mounted > with '-o dax=inode', advertise that the file is capable of per-file > DAX if the inode in the backend fs is marked with FS_DAX_FL flag. > > Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com> > --- > tools/virtiofsd/passthrough_ll.c | 43 ++++++++++++++++++++++++++++++++ > 1 file changed, 43 insertions(+) > > diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c > index 5b6228210f..4cbd904248 100644 > --- a/tools/virtiofsd/passthrough_ll.c > +++ b/tools/virtiofsd/passthrough_ll.c > @@ -171,6 +171,7 @@ struct lo_data { > int allow_direct_io; > int announce_submounts; > int perfile_dax_cap; /* capability of backend fs */ > + bool perfile_dax; /* enable per-file DAX or not */ > bool use_statx; > struct lo_inode root; > GHashTable *inodes; /* protected by lo->mutex */ > @@ -716,6 +717,10 @@ static void lo_init(void *userdata, struct fuse_conn_info *conn) > > if (conn->capable & FUSE_CAP_PERFILE_DAX && lo->perfile_dax_cap ) { > conn->want |= FUSE_CAP_PERFILE_DAX; > + lo->perfile_dax = 1; > + } > + else { > + lo->perfile_dax = 0; > } > } > > @@ -983,6 +988,41 @@ static int do_statx(struct lo_data *lo, int dirfd, const char *pathname, > return 0; > } > > +/* > + * If the file is marked with FS_DAX_FL or FS_XFLAG_DAX, then DAX should be > + * enabled for this file. > + */ > +static bool lo_should_enable_dax(struct lo_data *lo, struct lo_inode *dir, > + const char *name) > +{ > + int res, fd; > + int ret = false;; > + unsigned int attr; > + struct fsxattr xattr; > + > + if (!lo->perfile_dax) > + return false; > + > + /* Open file without O_PATH, so that ioctl can be called. */ > + fd = openat(dir->fd, name, O_NOFOLLOW); > + if (fd == -1) > + return false; Doesn't that defeat the whole benefit of using O_PATH - i.e. that we might stumble into a /dev node or something else we're not allowed to open? > + if (lo->perfile_dax_cap == DAX_CAP_FLAGS) { > + res = ioctl(fd, FS_IOC_GETFLAGS, &attr); > + if (!res && (attr & FS_DAX_FL)) > + ret = true; > + } > + else if (lo->perfile_dax_cap == DAX_CAP_XATTR) { > + res = ioctl(fd, FS_IOC_FSGETXATTR, &xattr); > + if (!res && (xattr.fsx_xflags & FS_XFLAG_DAX)) > + ret = true; > + } This all looks pretty expensive for each lookup. Dave > + close(fd); > + return ret; > +} > + > /* > * Increments nlookup on the inode on success. unref_inode_lolocked() must be > * called eventually to decrement nlookup again. If inodep is non-NULL, the > @@ -1038,6 +1078,9 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t parent, const char *name, > e->attr_flags |= FUSE_ATTR_SUBMOUNT; > } > > + if (lo_should_enable_dax(lo, dir, name)) > + e->attr_flags |= FUSE_ATTR_DAX; > + > inode = lo_find(lo, &e->attr, mnt_id); > if (inode) { > close(newfd); > -- > 2.27.0 > > _______________________________________________ > Virtio-fs mailing list > Virtio-fs@redhat.com > https://listman.redhat.com/mailman/listinfo/virtio-fs >
On 8/18/21 3:00 AM, Dr. David Alan Gilbert wrote: > * Jeffle Xu (jefflexu@linux.alibaba.com) wrote: >> For passthrough, when the corresponding virtiofs in guest is mounted >> with '-o dax=inode', advertise that the file is capable of per-file >> DAX if the inode in the backend fs is marked with FS_DAX_FL flag. >> >> Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com> >> --- >> tools/virtiofsd/passthrough_ll.c | 43 ++++++++++++++++++++++++++++++++ >> 1 file changed, 43 insertions(+) >> >> diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c >> index 5b6228210f..4cbd904248 100644 >> --- a/tools/virtiofsd/passthrough_ll.c >> +++ b/tools/virtiofsd/passthrough_ll.c >> @@ -171,6 +171,7 @@ struct lo_data { >> int allow_direct_io; >> int announce_submounts; >> int perfile_dax_cap; /* capability of backend fs */ >> + bool perfile_dax; /* enable per-file DAX or not */ >> bool use_statx; >> struct lo_inode root; >> GHashTable *inodes; /* protected by lo->mutex */ >> @@ -716,6 +717,10 @@ static void lo_init(void *userdata, struct fuse_conn_info *conn) >> >> if (conn->capable & FUSE_CAP_PERFILE_DAX && lo->perfile_dax_cap ) { >> conn->want |= FUSE_CAP_PERFILE_DAX; >> + lo->perfile_dax = 1; >> + } >> + else { >> + lo->perfile_dax = 0; >> } >> } >> >> @@ -983,6 +988,41 @@ static int do_statx(struct lo_data *lo, int dirfd, const char *pathname, >> return 0; >> } >> >> +/* >> + * If the file is marked with FS_DAX_FL or FS_XFLAG_DAX, then DAX should be >> + * enabled for this file. >> + */ >> +static bool lo_should_enable_dax(struct lo_data *lo, struct lo_inode *dir, >> + const char *name) >> +{ >> + int res, fd; >> + int ret = false;; >> + unsigned int attr; >> + struct fsxattr xattr; >> + >> + if (!lo->perfile_dax) >> + return false; >> + >> + /* Open file without O_PATH, so that ioctl can be called. */ >> + fd = openat(dir->fd, name, O_NOFOLLOW); >> + if (fd == -1) >> + return false; > > Doesn't that defeat the whole benefit of using O_PATH - i.e. that we > might stumble into a /dev node or something else we're not allowed to > open? As far as I know, virtiofsd will pivot_root/chroot to the source directory, and can only access files inside the source directory specified by "-o source=". Then where do these unexpected files come from? Besides, fd opened without O_PATH here is temporary and used for FS_IOC_GETFLAGS/FS_IOC_FSGETXATTR ioctl only. It's closed when the function returns. > >> + if (lo->perfile_dax_cap == DAX_CAP_FLAGS) { >> + res = ioctl(fd, FS_IOC_GETFLAGS, &attr); >> + if (!res && (attr & FS_DAX_FL)) >> + ret = true; >> + } >> + else if (lo->perfile_dax_cap == DAX_CAP_XATTR) { >> + res = ioctl(fd, FS_IOC_FSGETXATTR, &xattr); >> + if (!res && (xattr.fsx_xflags & FS_XFLAG_DAX)) >> + ret = true; >> + } > > This all looks pretty expensive for each lookup. Yes. it can be somehow optimized if we can agree on the way of storing the dax flag persistently.
* JeffleXu (jefflexu@linux.alibaba.com) wrote: > > > On 8/18/21 3:00 AM, Dr. David Alan Gilbert wrote: > > * Jeffle Xu (jefflexu@linux.alibaba.com) wrote: > >> For passthrough, when the corresponding virtiofs in guest is mounted > >> with '-o dax=inode', advertise that the file is capable of per-file > >> DAX if the inode in the backend fs is marked with FS_DAX_FL flag. > >> > >> Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com> > >> --- > >> tools/virtiofsd/passthrough_ll.c | 43 ++++++++++++++++++++++++++++++++ > >> 1 file changed, 43 insertions(+) > >> > >> diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c > >> index 5b6228210f..4cbd904248 100644 > >> --- a/tools/virtiofsd/passthrough_ll.c > >> +++ b/tools/virtiofsd/passthrough_ll.c > >> @@ -171,6 +171,7 @@ struct lo_data { > >> int allow_direct_io; > >> int announce_submounts; > >> int perfile_dax_cap; /* capability of backend fs */ > >> + bool perfile_dax; /* enable per-file DAX or not */ > >> bool use_statx; > >> struct lo_inode root; > >> GHashTable *inodes; /* protected by lo->mutex */ > >> @@ -716,6 +717,10 @@ static void lo_init(void *userdata, struct fuse_conn_info *conn) > >> > >> if (conn->capable & FUSE_CAP_PERFILE_DAX && lo->perfile_dax_cap ) { > >> conn->want |= FUSE_CAP_PERFILE_DAX; > >> + lo->perfile_dax = 1; > >> + } > >> + else { > >> + lo->perfile_dax = 0; > >> } > >> } > >> > >> @@ -983,6 +988,41 @@ static int do_statx(struct lo_data *lo, int dirfd, const char *pathname, > >> return 0; > >> } > >> > >> +/* > >> + * If the file is marked with FS_DAX_FL or FS_XFLAG_DAX, then DAX should be > >> + * enabled for this file. > >> + */ > >> +static bool lo_should_enable_dax(struct lo_data *lo, struct lo_inode *dir, > >> + const char *name) > >> +{ > >> + int res, fd; > >> + int ret = false;; > >> + unsigned int attr; > >> + struct fsxattr xattr; > >> + > >> + if (!lo->perfile_dax) > >> + return false; > >> + > >> + /* Open file without O_PATH, so that ioctl can be called. */ > >> + fd = openat(dir->fd, name, O_NOFOLLOW); > >> + if (fd == -1) > >> + return false; > > > > Doesn't that defeat the whole benefit of using O_PATH - i.e. that we > > might stumble into a /dev node or something else we're not allowed to > > open? > > As far as I know, virtiofsd will pivot_root/chroot to the source > directory, and can only access files inside the source directory > specified by "-o source=". Then where do these unexpected files come > from? Besides, fd opened without O_PATH here is temporary and used for > FS_IOC_GETFLAGS/FS_IOC_FSGETXATTR ioctl only. It's closed when the > function returns. The guest is still allowed to mknod. See: https://lists.gnu.org/archive/html/qemu-devel/2021-01/msg05461.html also it's legal to expose a root filesystem for a guest; the virtiofsd should *never* open a device other than O_PATH - and it's really tricky to do a check to see if it is a device in a race-free way. > > > >> + if (lo->perfile_dax_cap == DAX_CAP_FLAGS) { > >> + res = ioctl(fd, FS_IOC_GETFLAGS, &attr); > >> + if (!res && (attr & FS_DAX_FL)) > >> + ret = true; > >> + } > >> + else if (lo->perfile_dax_cap == DAX_CAP_XATTR) { > >> + res = ioctl(fd, FS_IOC_FSGETXATTR, &xattr); > >> + if (!res && (xattr.fsx_xflags & FS_XFLAG_DAX)) > >> + ret = true; > >> + } > > > > This all looks pretty expensive for each lookup. > > Yes. it can be somehow optimized if we can agree on the way of storing > the dax flag persistently. Dave > -- > Thanks, > Jeffle >
On 8/19/21 9:08 PM, Dr. David Alan Gilbert wrote: > * JeffleXu (jefflexu@linux.alibaba.com) wrote: >> >> >> On 8/18/21 3:00 AM, Dr. David Alan Gilbert wrote: >>> * Jeffle Xu (jefflexu@linux.alibaba.com) wrote: >>>> For passthrough, when the corresponding virtiofs in guest is mounted >>>> with '-o dax=inode', advertise that the file is capable of per-file >>>> DAX if the inode in the backend fs is marked with FS_DAX_FL flag. >>>> >>>> Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com> >>>> --- >>>> tools/virtiofsd/passthrough_ll.c | 43 ++++++++++++++++++++++++++++++++ >>>> 1 file changed, 43 insertions(+) >>>> >>>> diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c >>>> index 5b6228210f..4cbd904248 100644 >>>> --- a/tools/virtiofsd/passthrough_ll.c >>>> +++ b/tools/virtiofsd/passthrough_ll.c >>>> @@ -171,6 +171,7 @@ struct lo_data { >>>> int allow_direct_io; >>>> int announce_submounts; >>>> int perfile_dax_cap; /* capability of backend fs */ >>>> + bool perfile_dax; /* enable per-file DAX or not */ >>>> bool use_statx; >>>> struct lo_inode root; >>>> GHashTable *inodes; /* protected by lo->mutex */ >>>> @@ -716,6 +717,10 @@ static void lo_init(void *userdata, struct fuse_conn_info *conn) >>>> >>>> if (conn->capable & FUSE_CAP_PERFILE_DAX && lo->perfile_dax_cap ) { >>>> conn->want |= FUSE_CAP_PERFILE_DAX; >>>> + lo->perfile_dax = 1; >>>> + } >>>> + else { >>>> + lo->perfile_dax = 0; >>>> } >>>> } >>>> >>>> @@ -983,6 +988,41 @@ static int do_statx(struct lo_data *lo, int dirfd, const char *pathname, >>>> return 0; >>>> } >>>> >>>> +/* >>>> + * If the file is marked with FS_DAX_FL or FS_XFLAG_DAX, then DAX should be >>>> + * enabled for this file. >>>> + */ >>>> +static bool lo_should_enable_dax(struct lo_data *lo, struct lo_inode *dir, >>>> + const char *name) >>>> +{ >>>> + int res, fd; >>>> + int ret = false;; >>>> + unsigned int attr; >>>> + struct fsxattr xattr; >>>> + >>>> + if (!lo->perfile_dax) >>>> + return false; >>>> + >>>> + /* Open file without O_PATH, so that ioctl can be called. */ >>>> + fd = openat(dir->fd, name, O_NOFOLLOW); >>>> + if (fd == -1) >>>> + return false; >>> >>> Doesn't that defeat the whole benefit of using O_PATH - i.e. that we >>> might stumble into a /dev node or something else we're not allowed to >>> open? >> >> As far as I know, virtiofsd will pivot_root/chroot to the source >> directory, and can only access files inside the source directory >> specified by "-o source=". Then where do these unexpected files come >> from? Besides, fd opened without O_PATH here is temporary and used for >> FS_IOC_GETFLAGS/FS_IOC_FSGETXATTR ioctl only. It's closed when the >> function returns. > > The guest is still allowed to mknod. > See: > https://lists.gnu.org/archive/html/qemu-devel/2021-01/msg05461.html > > also it's legal to expose a root filesystem for a guest; the virtiofsd > should *never* open a device other than O_PATH - and it's really tricky > to do a check to see if it is a device in a race-free way. > Fine. Got it. However the returned fd (opened without O_PATH) is only used for FS_IOC_GETFLAGS/FS_IOC_FSGETXATTR ioctl, while in most cases for special device files, these two ioctls should return -ENOTTY. If it's really a security issue, then lo_inode_open() could be used to get a temporary fd, i.e., check if it's a special file before opening. After all, FUSE_OPEN also handles in this way. Besides, I can't understand what "race-free way" means.
On Fri, 20 Aug 2021 13:03:23 +0800 JeffleXu <jefflexu@linux.alibaba.com> wrote: > > > On 8/19/21 9:08 PM, Dr. David Alan Gilbert wrote: > > * JeffleXu (jefflexu@linux.alibaba.com) wrote: > >> > >> > >> On 8/18/21 3:00 AM, Dr. David Alan Gilbert wrote: > >>> * Jeffle Xu (jefflexu@linux.alibaba.com) wrote: > >>>> For passthrough, when the corresponding virtiofs in guest is mounted > >>>> with '-o dax=inode', advertise that the file is capable of per-file > >>>> DAX if the inode in the backend fs is marked with FS_DAX_FL flag. > >>>> > >>>> Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com> > >>>> --- > >>>> tools/virtiofsd/passthrough_ll.c | 43 ++++++++++++++++++++++++++++++++ > >>>> 1 file changed, 43 insertions(+) > >>>> > >>>> diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c > >>>> index 5b6228210f..4cbd904248 100644 > >>>> --- a/tools/virtiofsd/passthrough_ll.c > >>>> +++ b/tools/virtiofsd/passthrough_ll.c > >>>> @@ -171,6 +171,7 @@ struct lo_data { > >>>> int allow_direct_io; > >>>> int announce_submounts; > >>>> int perfile_dax_cap; /* capability of backend fs */ > >>>> + bool perfile_dax; /* enable per-file DAX or not */ > >>>> bool use_statx; > >>>> struct lo_inode root; > >>>> GHashTable *inodes; /* protected by lo->mutex */ > >>>> @@ -716,6 +717,10 @@ static void lo_init(void *userdata, struct fuse_conn_info *conn) > >>>> > >>>> if (conn->capable & FUSE_CAP_PERFILE_DAX && lo->perfile_dax_cap ) { > >>>> conn->want |= FUSE_CAP_PERFILE_DAX; > >>>> + lo->perfile_dax = 1; > >>>> + } > >>>> + else { > >>>> + lo->perfile_dax = 0; > >>>> } > >>>> } > >>>> > >>>> @@ -983,6 +988,41 @@ static int do_statx(struct lo_data *lo, int dirfd, const char *pathname, > >>>> return 0; > >>>> } > >>>> > >>>> +/* > >>>> + * If the file is marked with FS_DAX_FL or FS_XFLAG_DAX, then DAX should be > >>>> + * enabled for this file. > >>>> + */ > >>>> +static bool lo_should_enable_dax(struct lo_data *lo, struct lo_inode *dir, > >>>> + const char *name) > >>>> +{ > >>>> + int res, fd; > >>>> + int ret = false;; > >>>> + unsigned int attr; > >>>> + struct fsxattr xattr; > >>>> + > >>>> + if (!lo->perfile_dax) > >>>> + return false; > >>>> + > >>>> + /* Open file without O_PATH, so that ioctl can be called. */ > >>>> + fd = openat(dir->fd, name, O_NOFOLLOW); > >>>> + if (fd == -1) > >>>> + return false; > >>> > >>> Doesn't that defeat the whole benefit of using O_PATH - i.e. that we > >>> might stumble into a /dev node or something else we're not allowed to > >>> open? > >> > >> As far as I know, virtiofsd will pivot_root/chroot to the source > >> directory, and can only access files inside the source directory > >> specified by "-o source=". Then where do these unexpected files come > >> from? Besides, fd opened without O_PATH here is temporary and used for > >> FS_IOC_GETFLAGS/FS_IOC_FSGETXATTR ioctl only. It's closed when the > >> function returns. > > > > The guest is still allowed to mknod. > > See: > > https://lists.gnu.org/archive/html/qemu-devel/2021-01/msg05461.html > > > > also it's legal to expose a root filesystem for a guest; the virtiofsd > > should *never* open a device other than O_PATH - and it's really tricky > > to do a check to see if it is a device in a race-free way. > > > > Fine. Got it. However the returned fd (opened without O_PATH) is only > used for FS_IOC_GETFLAGS/FS_IOC_FSGETXATTR ioctl, while in most cases > for special device files, these two ioctls should return -ENOTTY. > The actual problem is that a FIFO will cause openat() to block until the other end of the FIFO is open for writing... > If it's really a security issue, then lo_inode_open() could be used to ... and cause a DoS on virtiofsd. So yes, this is a security issue and lo_inode_open() was introduced specifically to handle this. > get a temporary fd, i.e., check if it's a special file before opening. > After all, FUSE_OPEN also handles in this way. Besides, I can't > understand what "race-free way" means. > "race-free way" means a way that guarantees that file type cannot change between the time you check it and the time you open it (TOCTOU error). For example, doing a plain stat(), checking st_mode and proceeding to open() is wrong : nothing prevents the file to be unlinked and replaced by something else between stat() and open(). We avoid that by keeping O_PATH fds around and using lo_inode_open() instead of openat(). In your case, it seems that you should do the checking after you have an actual lo_inode for the target file, and pass that to lo_should_enable_dax() instead of the parent lo_inode and target name. Cheers, -- Greg
On 8/24/21 6:15 PM, Greg Kurz wrote: > On Fri, 20 Aug 2021 13:03:23 +0800 > JeffleXu <jefflexu@linux.alibaba.com> wrote: >> >> Fine. Got it. However the returned fd (opened without O_PATH) is only >> used for FS_IOC_GETFLAGS/FS_IOC_FSGETXATTR ioctl, while in most cases >> for special device files, these two ioctls should return -ENOTTY. >> > > The actual problem is that a FIFO will cause openat() to block until > the other end of the FIFO is open for writing... Got it. > >> If it's really a security issue, then lo_inode_open() could be used to > > ... and cause a DoS on virtiofsd. So yes, this is a security issue and > lo_inode_open() was introduced specifically to handle this. > >> get a temporary fd, i.e., check if it's a special file before opening. >> After all, FUSE_OPEN also handles in this way. Besides, I can't >> understand what "race-free way" means. >> > > "race-free way" means a way that guarantees that file type > cannot change between the time you check it and the time > you open it (TOCTOU error). For example, doing a plain stat(), > checking st_mode and proceeding to open() is wrong : nothing > prevents the file to be unlinked and replaced by something > else between stat() and open(). > > We avoid that by keeping O_PATH fds around and using > lo_inode_open() instead of openat(). Thanks for the detailed explanation. Got it. > > In your case, it seems that you should do the checking after > you have an actual lo_inode for the target file, and pass > that to lo_should_enable_dax() instead of the parent lo_inode > and target name. > Yes, that will be more reasonable. Thanks.
diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c index 5b6228210f..4cbd904248 100644 --- a/tools/virtiofsd/passthrough_ll.c +++ b/tools/virtiofsd/passthrough_ll.c @@ -171,6 +171,7 @@ struct lo_data { int allow_direct_io; int announce_submounts; int perfile_dax_cap; /* capability of backend fs */ + bool perfile_dax; /* enable per-file DAX or not */ bool use_statx; struct lo_inode root; GHashTable *inodes; /* protected by lo->mutex */ @@ -716,6 +717,10 @@ static void lo_init(void *userdata, struct fuse_conn_info *conn) if (conn->capable & FUSE_CAP_PERFILE_DAX && lo->perfile_dax_cap ) { conn->want |= FUSE_CAP_PERFILE_DAX; + lo->perfile_dax = 1; + } + else { + lo->perfile_dax = 0; } } @@ -983,6 +988,41 @@ static int do_statx(struct lo_data *lo, int dirfd, const char *pathname, return 0; } +/* + * If the file is marked with FS_DAX_FL or FS_XFLAG_DAX, then DAX should be + * enabled for this file. + */ +static bool lo_should_enable_dax(struct lo_data *lo, struct lo_inode *dir, + const char *name) +{ + int res, fd; + int ret = false;; + unsigned int attr; + struct fsxattr xattr; + + if (!lo->perfile_dax) + return false; + + /* Open file without O_PATH, so that ioctl can be called. */ + fd = openat(dir->fd, name, O_NOFOLLOW); + if (fd == -1) + return false; + + if (lo->perfile_dax_cap == DAX_CAP_FLAGS) { + res = ioctl(fd, FS_IOC_GETFLAGS, &attr); + if (!res && (attr & FS_DAX_FL)) + ret = true; + } + else if (lo->perfile_dax_cap == DAX_CAP_XATTR) { + res = ioctl(fd, FS_IOC_FSGETXATTR, &xattr); + if (!res && (xattr.fsx_xflags & FS_XFLAG_DAX)) + ret = true; + } + + close(fd); + return ret; +} + /* * Increments nlookup on the inode on success. unref_inode_lolocked() must be * called eventually to decrement nlookup again. If inodep is non-NULL, the @@ -1038,6 +1078,9 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t parent, const char *name, e->attr_flags |= FUSE_ATTR_SUBMOUNT; } + if (lo_should_enable_dax(lo, dir, name)) + e->attr_flags |= FUSE_ATTR_DAX; + inode = lo_find(lo, &e->attr, mnt_id); if (inode) { close(newfd);
For passthrough, when the corresponding virtiofs in guest is mounted with '-o dax=inode', advertise that the file is capable of per-file DAX if the inode in the backend fs is marked with FS_DAX_FL flag. Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com> --- tools/virtiofsd/passthrough_ll.c | 43 ++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+)