On 8/18/21 3:00 AM, Dr. David Alan Gilbert wrote:
> * Jeffle Xu (jefflexu@xxxxxxxxxxxxxxxxx) 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@xxxxxxxxxxxxxxxxx>
>> ---
>> 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.
--
Thanks,
Jeffle
