* [PATCH v2] virtiofsd: Add -o allow_direct_io|no_allow_direct_io options
@ 2020-08-24 10:59 Jiachen Zhang
2020-09-24 11:09 ` Dr. David Alan Gilbert
0 siblings, 1 reply; 2+ messages in thread
From: Jiachen Zhang @ 2020-08-24 10:59 UTC (permalink / raw)
To: Dr . David Alan Gilbert, Stefan Hajnoczi
Cc: Yongji Xie, Jiachen Zhang, qemu-devel
Due to the commit 65da4539803373ec4eec97ffc49ee90083e56efd, 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>
---
tools/virtiofsd/helper.c | 4 ++++
tools/virtiofsd/passthrough_ll.c | 20 ++++++++++++++------
2 files changed, 18 insertions(+), 6 deletions(-)
diff --git a/tools/virtiofsd/helper.c b/tools/virtiofsd/helper.c
index 3105b6c23a..45b310ff3c 100644
--- a/tools/virtiofsd/helper.c
+++ b/tools/virtiofsd/helper.c
@@ -180,6 +180,10 @@ 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"
);
}
diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
index 94e0de2d2b..c1ae897b77 100644
--- a/tools/virtiofsd/passthrough_ll.c
+++ b/tools/virtiofsd/passthrough_ll.c
@@ -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);
@@ -2824,6 +2831,7 @@ int main(int argc, char *argv[])
.debug = 0,
.writeback = 0,
.posix_lock = 1,
+ .allow_direct_io = 0,
.proc_self_fd = -1,
};
struct lo_map_elem *root_elem;
--
2.11.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH v2] virtiofsd: Add -o allow_direct_io|no_allow_direct_io options
2020-08-24 10:59 [PATCH v2] virtiofsd: Add -o allow_direct_io|no_allow_direct_io options Jiachen Zhang
@ 2020-09-24 11:09 ` Dr. David Alan Gilbert
0 siblings, 0 replies; 2+ messages in thread
From: Dr. David Alan Gilbert @ 2020-09-24 11:09 UTC (permalink / raw)
To: Jiachen Zhang; +Cc: Yongji Xie, qemu-devel, Stefan Hajnoczi
* Jiachen Zhang (zhangjiachen.jaycee@bytedance.com) wrote:
> Due to the commit 65da4539803373ec4eec97ffc49ee90083e56efd, 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>
Queued
> ---
> tools/virtiofsd/helper.c | 4 ++++
> tools/virtiofsd/passthrough_ll.c | 20 ++++++++++++++------
> 2 files changed, 18 insertions(+), 6 deletions(-)
>
> diff --git a/tools/virtiofsd/helper.c b/tools/virtiofsd/helper.c
> index 3105b6c23a..45b310ff3c 100644
> --- a/tools/virtiofsd/helper.c
> +++ b/tools/virtiofsd/helper.c
> @@ -180,6 +180,10 @@ 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"
> );
> }
>
> diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
> index 94e0de2d2b..c1ae897b77 100644
> --- a/tools/virtiofsd/passthrough_ll.c
> +++ b/tools/virtiofsd/passthrough_ll.c
> @@ -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);
> @@ -2824,6 +2831,7 @@ int main(int argc, char *argv[])
> .debug = 0,
> .writeback = 0,
> .posix_lock = 1,
> + .allow_direct_io = 0,
> .proc_self_fd = -1,
> };
> struct lo_map_elem *root_elem;
> --
> 2.11.0
>
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
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