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virtiofsd: Add -o allow_direct_io|no_allow_direct_io options 

Due to the commit 65da453980, 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 use direct I/O, we no longer have any chance to bypass the
host page cache.

Therefore, we add a flag 'allow_direct_io' to lo_data. If '-o
 no_allow_direct_io' option is added, or none of '-o allow_direct_io' or
 '-o no_allow_direct_io' is added, the 'allow_direct_io' will be set to
 0, and virtiofsd discards O_DIRECT as before. If '-o allow_direct_io'
is added to the starting command-line, 'allow_direct_io' 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.jaycee@bytedance.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20200824105957.61265-1-zhangjiachen.jaycee@bytedance.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
This commit is contained in:
Jiachen Zhang 2020-08-24 18:59:57 +08:00 committed by Dr. David Alan Gilbert
parent 04d325e86f
commit e12a0edafe
2 changed files with 18 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
tools/virtiofsd/helper.c
View File

@ -178,6 +178,10 @@ 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_direct_io|no_allow_direct_io\n"
" retain/discard O_DIRECT flags passed down\n"
" to virtiofsd from guest applications.\n"
" default: no_allow_direct_io\n"
);
}

20
tools/virtiofsd/passthrough_ll.c
View File

@ -151,6 +151,7 @@ struct lo_data {
int timeout_set;
int readdirplus_set;
int readdirplus_clear;
int allow_direct_io;
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_direct_io", offsetof(struct lo_data, allow_direct_io), 1 },
{ "no_allow_direct_io", offsetof(struct lo_data, allow_direct_io), 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_direct_io,
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_allow_direct_io'). If somebody needs that behavior,
* the '-o allow_direct_io' option should be set.
*/
fi->flags &= ~O_DIRECT;
if (!allow_direct_io) {
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_direct_io, 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_direct_io, fi);
sprintf(buf, "%i", lo_fd(req, ino));
fd = openat(lo->proc_self_fd, buf, fi->flags & ~O_NOFOLLOW);
@ -2823,6 +2830,7 @@ int main(int argc, char *argv[])
.debug = 0,
.writeback = 0,
.posix_lock = 0,
.allow_direct_io = 0,
.proc_self_fd = -1,
};
struct lo_map_elem *root_elem;