On Tue, Sep 01, 2020 at 04:40:43PM -0400, Vivek Goyal wrote: > Hi, > > I want to enable SB_NOSEC in fuse in some form so that performance of > small random writes can be improved. As of now, we call file_remove_privs(), > which results in fuse always sending getxattr(security.capability) to > server to figure out if security.capability has been set on file or not. > If it has been set, it needs to be cleared. This slows down small > random writes tremendously. > > I posted couple of proposals in the past here. > > Proposal 1: > > https://lore.kernel.org/linux-fsdevel/20200716144032.GC422759@xxxxxxxxxx/ > > Proposal 2: > > https://lore.kernel.org/linux-fsdevel/20200724183812.19573-1-vgoyal@xxxxxxxxxx/ > > This is 3rd proposal now. One of the roadblocks in enabling SB_NOSEC > is shared filesystem. It is possible that another client modified the > file data and this client does not know about it. So we might regress > if we don't fetch security.capability always. > > So looks like this needs to be handled different for shared filesystems > and non-shared filesystems. non-shared filesystems will be more like > local filesystems where fuse does not expect file data/metadata to > change outside the fuse. And we should be able to enable SB_NOSEC > optimization. This is what this proposal does. > > It does not handle the case of shared filesystems. I believe solution > to that will depend on filesystem based on what's the cache coherency > guarantees filesystem provides and what's the cache invalidation > mechanism it uses. > > For now, all filesystems which are not shared can benefit from this > optimization. I am interested in virtiofs which is not shared in > many of the cases. In fact we don't even support shared mode yet. Here is the corresponding qemu virtiofsd patch which can enable this feature. Subject: virtiofsd: Enable FUSE_NONSHARED_FS by default Set FUSE_NONSHARED_FS flag by default as we don't support sharing of virtiofs filesystem yet. Once that is supported, it should not be set for shared mode. Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx> --- include/standard-headers/linux/fuse.h | 4 ++++ tools/virtiofsd/fuse_lowlevel.c | 9 +++++++++ 2 files changed, 13 insertions(+) Index: qemu/include/standard-headers/linux/fuse.h =================================================================== --- qemu.orig/include/standard-headers/linux/fuse.h 2020-09-01 15:22:31.449707002 -0400 +++ qemu/include/standard-headers/linux/fuse.h 2020-09-01 15:23:18.776668542 -0400 @@ -172,6 +172,8 @@ * - add FUSE_WRITE_KILL_PRIV flag * - add FUSE_SETUPMAPPING and FUSE_REMOVEMAPPING * - add map_alignment to fuse_init_out, add FUSE_MAP_ALIGNMENT flag + * 7.32 + * - add FUSE_NONSHARED_FS flag */ #ifndef _LINUX_FUSE_H @@ -310,6 +312,7 @@ struct fuse_file_lock { * FUSE_NO_OPENDIR_SUPPORT: kernel supports zero-message opendir * FUSE_EXPLICIT_INVAL_DATA: only invalidate cached pages on explicit request * FUSE_MAP_ALIGNMENT: map_alignment field is valid + * FUSE_NONSHARED_FS: Filesystem is not shared. */ #define FUSE_ASYNC_READ (1 << 0) #define FUSE_POSIX_LOCKS (1 << 1) @@ -338,6 +341,7 @@ struct fuse_file_lock { #define FUSE_NO_OPENDIR_SUPPORT (1 << 24) #define FUSE_EXPLICIT_INVAL_DATA (1 << 25) #define FUSE_MAP_ALIGNMENT (1 << 26) +#define FUSE_NONSHARED_FS (1 << 27) /** * CUSE INIT request/reply flags Index: qemu/tools/virtiofsd/fuse_lowlevel.c =================================================================== --- qemu.orig/tools/virtiofsd/fuse_lowlevel.c 2020-09-01 15:22:31.449707002 -0400 +++ qemu/tools/virtiofsd/fuse_lowlevel.c 2020-09-01 15:23:18.777668583 -0400 @@ -2218,6 +2218,15 @@ static void do_init(fuse_req_t req, fuse outarg.map_alignment = ffsl(sysconf(_SC_PAGE_SIZE)) - 1; } + if (arg->flags & FUSE_NONSHARED_FS) { + /* + * By default virtiofs is not shared. Once we support sharing, + * this will be have to a conditional and driven by user's + * selection. + */ + outarg.flags |= FUSE_NONSHARED_FS; + } + fuse_log(FUSE_LOG_DEBUG, " INIT: %u.%u\n", outarg.major, outarg.minor); fuse_log(FUSE_LOG_DEBUG, " flags=0x%08x\n", outarg.flags); fuse_log(FUSE_LOG_DEBUG, " max_readahead=0x%08x\n", outarg.max_readahead);
