[RFC PATCH] First RFC version of a new cache=mmap model.

[RFC PATCH] First RFC version of a new cache=mmap model.

[Dominique Martinet]

 - Add cache=mmap option
 - Try to keep most operations synchronous

Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
---

Hi,

I brought up the issue of mmap being read-only with cache=none a bit
ago, and worked on it since.

Here's what this patch does:
 - Add an option cache=mmap (or just mmap, like other caches), nothing
changes for default or other caches.
The following assumes cache=mmap.
 - fills in writeback_fid on open (this could be done in
v9fs_file_mmap since we don't enable buffered write either, but I
wanted to keep the code shared with other caches, so we just have
useless writeback fids most of the time)
 - flush mmap data synchronously on munmap (vma->vm_op->close), this
is because we don't want to use the cache for read, so we need the
modifications to take place immediately. I'm not quite sure why I had
to force it, but it's lost otherwise (with buffered reads, you'd read
from the mmap pages anyway and it wouldn't matter if it's flushed
later - this doesn't really work for this case)


What works:
 - msync(addr, length, MS_SYNC) (MS_SYNC might just be the default
behaviour) does sync correctly;
 - munmap does a sync as well, obviously;
 - no msync/msync with MS_ASYNC will eventually flush when the kernel
decides to.

What doesn't:
 - If you want to read a file after writting in a mmap'd section with
no msync (or msync with MS_ASYNC) and no munmap, you will read what
the servers  knows about -- so the old data. With buffered read,
you'd expect the read to find about the map and use it, we don't.
There is, however, what the documentation says so I don't see this as
a bug. What could probably be done would be to check on read if we
have dirty mapped pages and flush them before reading? I'm not too
sure I like this idea.
 - Likewise, if you write with a map open, the map won't be updated
unless something else invalidates it. I guess we should do that like
the direct write function does. 


All in all, while I'm unhappy that I had to use write_inode_now() in
vm_ops->close, I would guess it works for what it is (i.e. an unsafe
feature on a networking filesystem); at least it seems better than
returning ENOTSUPP for my own usage, given read mmap isn't much safer
anyway, and that's why it's an option.


There are a few questions/TODO marks and p9_debug lines that could go
away, but figured it probably makes more sense to leave it there for
an RFC patch.
(Also a few lines over 80 characters I'll fix for the real deal)


Comments more than welcome, thanks!


 fs/9p/v9fs.c           |  9 ++++-
 fs/9p/v9fs.h           |  1 +
 fs/9p/v9fs_vfs.h       |  2 ++
 fs/9p/vfs_addr.c       |  7 ++++
 fs/9p/vfs_file.c       | 95 ++++++++++++++++++++++++++++++++++++++++++++++++--
 fs/9p/vfs_inode.c      | 17 +++++----
 fs/9p/vfs_inode_dotl.c |  6 ++--
 fs/9p/vfs_super.c      |  5 +--
 8 files changed, 127 insertions(+), 15 deletions(-)

diff --git a/fs/9p/v9fs.c b/fs/9p/v9fs.c
index 58e6cbc..1a2b0c8 100644
--- a/fs/9p/v9fs.c
+++ b/fs/9p/v9fs.c
@@ -56,7 +56,7 @@ enum {
 	/* Options that take no arguments */
 	Opt_nodevmap,
 	/* Cache options */
-	Opt_cache_loose, Opt_fscache,
+	Opt_cache_loose, Opt_fscache, Opt_mmap,
 	/* Access options */
 	Opt_access, Opt_posixacl,
 	/* Error token */
@@ -74,6 +74,7 @@ static const match_table_t tokens = {
 	{Opt_cache, "cache=%s"},
 	{Opt_cache_loose, "loose"},
 	{Opt_fscache, "fscache"},
+	{Opt_mmap, "mmap"},
 	{Opt_cachetag, "cachetag=%s"},
 	{Opt_access, "access=%s"},
 	{Opt_posixacl, "posixacl"},
@@ -91,6 +92,9 @@ static int get_cache_mode(char *s)
 	} else if (!strcmp(s, "fscache")) {
 		version = CACHE_FSCACHE;
 		p9_debug(P9_DEBUG_9P, "Cache mode: fscache\n");
+	} else if (!strcmp(s, "mmap")) {
+		version = CACHE_MMAP;
+		p9_debug(P9_DEBUG_9P, "Cache mode: mmap\n");
 	} else if (!strcmp(s, "none")) {
 		version = CACHE_NONE;
 		p9_debug(P9_DEBUG_9P, "Cache mode: none\n");
@@ -220,6 +224,9 @@ static int v9fs_parse_options(struct v9fs_session_info *v9ses, char *opts)
 		case Opt_fscache:
 			v9ses->cache = CACHE_FSCACHE;
 			break;
+		case Opt_mmap:
+			v9ses->cache = CACHE_MMAP;
+			break;
 		case Opt_cachetag:
 #ifdef CONFIG_9P_FSCACHE
 			v9ses->cachetag = match_strdup(&args[0]);
diff --git a/fs/9p/v9fs.h b/fs/9p/v9fs.h
index a8e127c..099c771 100644
--- a/fs/9p/v9fs.h
+++ b/fs/9p/v9fs.h
@@ -64,6 +64,7 @@ enum p9_session_flags {
 
 enum p9_cache_modes {
 	CACHE_NONE,
+	CACHE_MMAP,
 	CACHE_LOOSE,
 	CACHE_FSCACHE,
 };
diff --git a/fs/9p/v9fs_vfs.h b/fs/9p/v9fs_vfs.h
index dc95a25..b83ebfb 100644
--- a/fs/9p/v9fs_vfs.h
+++ b/fs/9p/v9fs_vfs.h
@@ -50,6 +50,8 @@ extern const struct dentry_operations v9fs_dentry_operations;
 extern const struct dentry_operations v9fs_cached_dentry_operations;
 extern const struct file_operations v9fs_cached_file_operations;
 extern const struct file_operations v9fs_cached_file_operations_dotl;
+extern const struct file_operations v9fs_mmap_file_operations;
+extern const struct file_operations v9fs_mmap_file_operations_dotl;
 extern struct kmem_cache *v9fs_inode_cache;
 
 struct inode *v9fs_alloc_inode(struct super_block *sb);
diff --git a/fs/9p/vfs_addr.c b/fs/9p/vfs_addr.c
index 9ff073f..c71e886 100644
--- a/fs/9p/vfs_addr.c
+++ b/fs/9p/vfs_addr.c
@@ -202,6 +202,8 @@ static int v9fs_vfs_writepage(struct page *page, struct writeback_control *wbc)
 {
 	int retval;
 
+	p9_debug(P9_DEBUG_VFS, "page %p\n", page);
+
 	retval = v9fs_vfs_writepage_locked(page);
 	if (retval < 0) {
 		if (retval == -EAGAIN) {
@@ -282,6 +284,9 @@ static int v9fs_write_begin(struct file *filp, struct address_space *mapping,
 	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
 	struct inode *inode = mapping->host;
 
+
+	p9_debug(P9_DEBUG_VFS, "filp %p, mapping %p\n", filp, mapping);
+
 	v9inode = V9FS_I(inode);
 start:
 	page = grab_cache_page_write_begin(mapping, index, flags);
@@ -312,6 +317,8 @@ static int v9fs_write_end(struct file *filp, struct address_space *mapping,
 	loff_t last_pos = pos + copied;
 	struct inode *inode = page->mapping->host;
 
+	p9_debug(P9_DEBUG_VFS, "filp %p, mapping %p\n", filp, mapping);
+
 	if (unlikely(copied < len)) {
 		/*
 		 * zero out the rest of the area
diff --git a/fs/9p/vfs_file.c b/fs/9p/vfs_file.c
index d384a8b..666a08e 100644
--- a/fs/9p/vfs_file.c
+++ b/fs/9p/vfs_file.c
@@ -45,6 +45,7 @@
 #include "cache.h"
 
 static const struct vm_operations_struct v9fs_file_vm_ops;
+static const struct vm_operations_struct v9fs_mmap_file_vm_ops;
 
 /**
  * v9fs_file_open - open a file (or directory)
@@ -106,7 +107,9 @@ int v9fs_file_open(struct inode *inode, struct file *file)
 	}
 	mutex_unlock(&v9inode->v_mutex);
 #ifdef CONFIG_9P_FSCACHE
-	if (v9ses->cache)
+	/* previous check would also set cookie with CACHE_LOOSE?
+	 * set_cookie does a check if v9inode->fscache anyway... */
+	if (v9ses->cache == CACHE_FSCACHE)
 		v9fs_cache_inode_set_cookie(inode, file);
 #endif
 	return 0;
@@ -583,17 +586,33 @@ int v9fs_file_fsync_dotl(struct file *filp, loff_t start, loff_t end,
 }
 
 static int
-v9fs_file_mmap(struct file *file, struct vm_area_struct *vma)
+v9fs_file_mmap(struct file *filp, struct vm_area_struct *vma)
 {
 	int retval;
 
-	retval = generic_file_mmap(file, vma);
+
+	retval = generic_file_mmap(filp, vma);
 	if (!retval)
 		vma->vm_ops = &v9fs_file_vm_ops;
 
 	return retval;
 }
 
+/* TODO: merge this with the previous function
+ * and set the right vm_ops depending on v9ses->cache */
+static int
+v9fs_mmap_file_mmap(struct file *filp, struct vm_area_struct *vma)
+{
+	int retval;
+
+
+	retval = generic_file_mmap(filp, vma);
+	if (!retval)
+		vma->vm_ops = &v9fs_mmap_file_vm_ops;
+
+	return retval;
+}
+
 static int
 v9fs_vm_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
@@ -662,6 +681,22 @@ v9fs_cached_file_read(struct file *filp, char __user *data, size_t count,
 	return do_sync_read(filp, data, count, offset);
 }
 
+/**
+ * v9fs_mmap_file_read - read from a file
+ * @filp: file pointer to read
+ * @udata: user data buffer to read data into
+ * @count: size of buffer
+ * @offset: offset at which to read data
+ *
+ */
+static ssize_t
+v9fs_mmap_file_read(struct file *filp, char __user *data, size_t count,
+		      loff_t *offset)
+{
+	/* TODO: Check if there are dirty pages */
+	return v9fs_file_read(filp, data, count, offset);
+}
+
 static ssize_t
 v9fs_direct_write(struct file *filp, const char __user * data,
 		  size_t count, loff_t *offsetp)
@@ -732,12 +767,43 @@ v9fs_cached_file_write(struct file *filp, const char __user * data,
 	return do_sync_write(filp, data, count, offset);
 }
 
+
+/**
+ * v9fs_mmap_file_write - write to a file
+ * @filp: file pointer to write
+ * @data: data buffer to write data from
+ * @count: size of buffer
+ * @offset: offset at which to write data
+ *
+ */
+static ssize_t
+v9fs_mmap_file_write(struct file *filp, const char __user *data,
+		       size_t count, loff_t *offset)
+{
+	/* TODO: invalidate mmaps on filp's inode between offset and offset+count */
+	return v9fs_file_write(filp, data, count, offset);
+}
+
+static void v9fs_mmap_vm_close(struct vm_area_struct *vma)
+{
+	p9_debug(P9_DEBUG_VFS, "9p VMA close, %p, flushing", vma);
+	write_inode_now(file_inode(vma->vm_file), 1);
+}
+
+
 static const struct vm_operations_struct v9fs_file_vm_ops = {
 	.fault = filemap_fault,
 	.page_mkwrite = v9fs_vm_page_mkwrite,
 	.remap_pages = generic_file_remap_pages,
 };
 
+static const struct vm_operations_struct v9fs_mmap_file_vm_ops = {
+	.close = v9fs_mmap_vm_close,
+	.fault = filemap_fault,
+	.page_mkwrite = v9fs_vm_page_mkwrite,
+	.remap_pages = generic_file_remap_pages,
+};
+
 
 const struct file_operations v9fs_cached_file_operations = {
 	.llseek = generic_file_llseek,
@@ -788,3 +854,26 @@ const struct file_operations v9fs_file_operations_dotl = {
 	.mmap = generic_file_readonly_mmap,
 	.fsync = v9fs_file_fsync_dotl,
 };
+
+const struct file_operations v9fs_mmap_file_operations = {
+	.llseek = generic_file_llseek,
+	.read = v9fs_mmap_file_read,
+	.write = v9fs_mmap_file_write,
+	.open = v9fs_file_open,
+	.release = v9fs_dir_release,
+	.lock = v9fs_file_lock,
+	.mmap = v9fs_mmap_file_mmap,
+	.fsync = v9fs_file_fsync,
+};
+
+const struct file_operations v9fs_mmap_file_operations_dotl = {
+	.llseek = generic_file_llseek,
+	.read = v9fs_mmap_file_read,
+	.write = v9fs_mmap_file_write,
+	.open = v9fs_file_open,
+	.release = v9fs_dir_release,
+	.lock = v9fs_file_lock_dotl,
+	.flock = v9fs_file_flock_dotl,
+	.mmap = v9fs_mmap_file_mmap,
+	.fsync = v9fs_file_fsync_dotl,
+};
diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
index 25b018e..d52179c 100644
--- a/fs/9p/vfs_inode.c
+++ b/fs/9p/vfs_inode.c
@@ -299,15 +299,20 @@ int v9fs_init_inode(struct v9fs_session_info *v9ses,
 	case S_IFREG:
 		if (v9fs_proto_dotl(v9ses)) {
 			inode->i_op = &v9fs_file_inode_operations_dotl;
-			if (v9ses->cache)
+			if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
 				inode->i_fop =
 					&v9fs_cached_file_operations_dotl;
+			else if (v9ses->cache == CACHE_MMAP)
+				inode->i_fop = &v9fs_mmap_file_operations_dotl;
 			else
 				inode->i_fop = &v9fs_file_operations_dotl;
 		} else {
 			inode->i_op = &v9fs_file_inode_operations;
-			if (v9ses->cache)
-				inode->i_fop = &v9fs_cached_file_operations;
+			if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
+				inode->i_fop =
+					&v9fs_cached_file_operations;
+			else if (v9ses->cache == CACHE_MMAP)
+				inode->i_fop = &v9fs_mmap_file_operations;
 			else
 				inode->i_fop = &v9fs_file_operations;
 		}
@@ -816,7 +821,7 @@ struct dentry *v9fs_vfs_lookup(struct inode *dir, struct dentry *dentry,
 	 * unlink. For cached mode create calls request for new
 	 * inode. But with cache disabled, lookup should do this.
 	 */
-	if (v9ses->cache)
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
 		inode = v9fs_get_inode_from_fid(v9ses, fid, dir->i_sb);
 	else
 		inode = v9fs_get_new_inode_from_fid(v9ses, fid, dir->i_sb);
@@ -906,7 +911,7 @@ v9fs_vfs_atomic_open(struct inode *dir, struct dentry *dentry,
 
 	file->private_data = fid;
 #ifdef CONFIG_9P_FSCACHE
-	if (v9ses->cache)
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
 		v9fs_cache_inode_set_cookie(dentry->d_inode, file);
 #endif
 
@@ -1485,7 +1490,7 @@ int v9fs_refresh_inode(struct p9_fid *fid, struct inode *inode)
 	 */
 	i_size = inode->i_size;
 	v9fs_stat2inode(st, inode, inode->i_sb);
-	if (v9ses->cache)
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
 		inode->i_size = i_size;
 	spin_unlock(&inode->i_lock);
 out:
diff --git a/fs/9p/vfs_inode_dotl.c b/fs/9p/vfs_inode_dotl.c
index 53687bb..710d5c6 100644
--- a/fs/9p/vfs_inode_dotl.c
+++ b/fs/9p/vfs_inode_dotl.c
@@ -362,7 +362,7 @@ v9fs_vfs_atomic_open_dotl(struct inode *dir, struct dentry *dentry,
 		goto err_clunk_old_fid;
 	file->private_data = ofid;
 #ifdef CONFIG_9P_FSCACHE
-	if (v9ses->cache)
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
 		v9fs_cache_inode_set_cookie(inode, file);
 #endif
 	*opened |= FILE_CREATED;
@@ -725,7 +725,7 @@ v9fs_vfs_symlink_dotl(struct inode *dir, struct dentry *dentry,
 	}
 
 	v9fs_invalidate_inode_attr(dir);
-	if (v9ses->cache) {
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE) {
 		/* Now walk from the parent so we can get an unopened fid. */
 		fid = p9_client_walk(dfid, 1, &name, 1);
 		if (IS_ERR(fid)) {
@@ -983,7 +983,7 @@ int v9fs_refresh_inode_dotl(struct p9_fid *fid, struct inode *inode)
 	 */
 	i_size = inode->i_size;
 	v9fs_stat2inode_dotl(st, inode);
-	if (v9ses->cache)
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
 		inode->i_size = i_size;
 	spin_unlock(&inode->i_lock);
 out:
diff --git a/fs/9p/vfs_super.c b/fs/9p/vfs_super.c
index 2756dcd..60e5763 100644
--- a/fs/9p/vfs_super.c
+++ b/fs/9p/vfs_super.c
@@ -282,7 +282,7 @@ static int v9fs_drop_inode(struct inode *inode)
 {
 	struct v9fs_session_info *v9ses;
 	v9ses = v9fs_inode2v9ses(inode);
-	if (v9ses->cache)
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
 		return generic_drop_inode(inode);
 	/*
 	 * in case of non cached mode always drop the
@@ -325,10 +325,11 @@ static int v9fs_write_inode_dotl(struct inode *inode,
 	 * send an fsync request to server irrespective of
 	 * wbc->sync_mode.
 	 */
-	p9_debug(P9_DEBUG_VFS, "%s: inode %p\n", __func__, inode);
 	v9inode = V9FS_I(inode);
+	p9_debug(P9_DEBUG_VFS, "%s: inode %p, writeback_fid %p\n", __func__, inode, v9inode->writeback_fid);
 	if (!v9inode->writeback_fid)
 		return 0;
+
 	ret = p9_client_fsync(v9inode->writeback_fid, 0);
 	if (ret < 0) {
 		__mark_inode_dirty(inode, I_DIRTY_DATASYNC);
-- 
1.8.1.4

Re: [RFC PATCH] First RFC version of a new cache=mmap model.

[MARTINET Dominique]

On 09/03/13 16:24, Eric Van Hensbergen wrote:
> Interesting, do me a favor and cross-post to at least linux-fsdevel --
> there have been some strong objections from the rest of the community on
> similar approaches in the past, and I'd rather we encounter them earlier
> rather than when I try to push the patch upstream.  The lack of
> consistency is pretty nasty, we'll need a big disclaimer in the
> documentation if we decide to take it forward.  You may also want to
> cross-check some of my earlier efforts (back in 2.6.14 timeframe IIRC)
> if you haven't already.  I had some hackery to try and force things
> through sooner.

Right, sorry about this, reposted it to everyone right now.

> FWIW, the right approach is probably to try and go for some more
> intelligent caching mechanism based on revokable leases so that the
> server can force a flush on a client if necessary -- but I understand
> that's a pretty big nut to crack and if this solves for your use case
> perhaps its the right start.

I tried to enable cached read/writes to keep the original behaviour, but 
it pretty quickly turns back into a cache=loose without metadata 
behaviour and I wanted to avoid this - the less cached the better as far 
as I'm concerned.

I'm also working on a 9P server (nfs-ganesha, 
https://github.com/nfs-ganesha/nfs-ganesha ), so breaking the server 
definitely isn't out of question.
Something based on lock/getlock might be possible but I don't think 
there is anything in the protocol that would make them revokable, 
especially since every message originates from the client...
If anything, I'd rather check before reading or writing if we have dirty 
pages to avoid inconsistencies with other filesystems.

-- 
Dominique

Re: [V9fs-developer] [RFC PATCH] First RFC version of a new cache=mmap model.

[Rob Landley]

On 09/03/2013 09:37:58 AM, Dominique Martinet wrote:
>  - Add cache=mmap option
>  - Try to keep most operations synchronous
> 
> Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
> ---
> 
> Hi,
> 
> I brought up the issue of mmap being read-only with cache=none a bit
> ago, and worked on it since.
> 
> Here's what this patch does:
>  - Add an option cache=mmap (or just mmap, like other caches), nothing
> changes for default or other caches.

Interesting.

Should this become the default behavior instead of "none" for  
non-readonly mounts? (What's the point of the "none" mode now that we  
have writeable mmap implemented, is there any advantage?)

Rob

Re: [V9fs-developer] [RFC PATCH] First RFC version of a new cache=mmap model.

[Dominique Martinet]

Hi,

Rob Landley wrote on Sat, Sep 07, 2013 :
> On 09/03/2013 09:37:58 AM, Dominique Martinet wrote:
> >  - Add cache=mmap option
> >  - Try to keep most operations synchronous
> > 
> > Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
> > ---
> > 
> > Hi,
> > 
> > I brought up the issue of mmap being read-only with cache=none a bit
> > ago, and worked on it since.
> > 
> > Here's what this patch does:
> >  - Add an option cache=mmap (or just mmap, like other caches), nothing
> > changes for default or other caches.
> 
> Interesting.
> 
> Should this become the default behavior instead of "none" for  
> non-readonly mounts? (What's the point of the "none" mode now that we  
> have writeable mmap implemented, is there any advantage?)

Well, if there is no issue with the principle of flushing the map on
close, it might eventually become more widely used and maybe the
default.

I don't think there should be any inconsistency with what the
documentation says mmap should do, but this doesn't mean everything will
work as expected and it's not because this passes all the tests I tried
that it won't break anything (and in a very subtle way that would
silently corrupt data, so definitely not something we want)

This definitely needs some consideration/more reviews and, in my
opinion, much more testing before pretending to get there.


By the way, two more questions from my end, if anyone can help:
 - the mkwrite function calls "v9fs_fscache_wait_on_page_write(inode,
page);". I'm afraid I don't understand why we need to wait that
everything has been flushed before we make the page writable, what does
it do? Check the the page doesn't need to be invalidated/re-read before
the actual edits, so as not to cause corruptions around the edited
parts? Does mkwrite require/imply exclusive access to the modified
pages?

 - given that we have the vm_area_struct we are closing, for the flush,
would we have any better call than "write_inode_now" on the whole inode
since we ought to know which pages are concerned by the vma? (think
about a file with many mmaps on different parts of the file, we don't
want to flush it all everytime)


Would also appreciate comments from maintainers/anyone before I repost a
clean patch to push through, might as well fix things as early as
possible :)


Thanks,
-- 
Dominique

[RFC PATCH V2] RFC version of a new cache=mmap model.

[Dominique Martinet]

 - Add cache=mmap option
 - Try to keep most operations synchronous

Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
---

Changes from V1 to V2:
 - Changed write_inode_now to sync_inode with the specific region
relating the mmap'd area (I'm honestly not sure about bounds, but it
covers at least the area pointed by the vma_struct. There doesn't seem
to be many functions using sync_inode, should I use do_writeback
directly instead? does it still make sense to check
mapping_cap_writeback_dirty on inode mapping when I'm using sync on a
sub-range?)
 - Fixed one v9ses->cache check that kept inodes around in cache

Missing for offering a real patch:
 - I didn't get any reply on what v9fs_fscache_wait_on_page_write
is called for, so mkwrite might still be wrong given it technically
doesn't wait for anything.
 - I originally wanted to open writeback fids at the same places as
the other cache modems, but it does seem like a waste and will move it
to the mmap creation call; a shame to duplicate code but there really
were many unused fids open because of this
 - More complains/comments :)




Original comment:
I brought up the issue of mmap being read-only with cache=none a bit
ago, and worked on it since.

Here's what this patch does:
 - Add an option cache=mmap (or just mmap, like other caches), nothing
changes for default or other caches.
The following assumes cache=mmap.
 - fills in writeback_fid on open (this could be done in
v9fs_file_mmap since we don't enable buffered write either, but I
wanted to keep the code shared with other caches, so we just have
useless writeback fids most of the time)
 - flush mmap data synchronously on munmap (vma->vm_op->close), this
is because we don't want to use the cache for read, so we need the
modifications to take place immediately. I'm not quite sure why I had
to force it, but it's lost otherwise (with buffered reads, you'd read
from the mmap pages anyway and it wouldn't matter if it's flushed
later - this doesn't really work for this case)


What works:
 - msync(addr, length, MS_SYNC) (MS_SYNC might just be the default
behaviour) does sync correctly;
 - munmap does a sync as well, obviously;
 - no msync/msync with MS_ASYNC will eventually flush when the kernel
decides to.

What doesn't:
 - If you want to read a file after writting in a mmap'd section with
no msync (or msync with MS_ASYNC) and no munmap, you will read what
the servers  knows about -- so the old data. With buffered read,
you'd expect the read to find about the map and use it, we don't.
There is, however, what the documentation says so I don't see this as
a bug. What could probably be done would be to check on read if we
have dirty mapped pages and flush them before reading? I'm not too
sure I like this idea.
 - Likewise, if you write with a map open, the map won't be updated
unless something else invalidates it. I guess we should do that like
the direct write function does.


All in all, while I'm unhappy that I had to use write_inode_now() in
vm_ops->close, I would guess it works for what it is (i.e. an unsafe
feature on a networking filesystem); at least it seems better than
returning ENOTSUPP for my own usage, given read mmap isn't much safer
anyway, and that's why it's an option.


There are a few questions/TODO marks and p9_debug lines that could go
away, but figured it probably makes more sense to leave it there for
an RFC patch.
(Also a few lines over 80 characters I'll fix for the real deal)


Comments more than welcome, thanks!


 fs/9p/v9fs.c           |   9 +++-
 fs/9p/v9fs.h           |   1 +
 fs/9p/v9fs_vfs.h       |   2 +
 fs/9p/vfs_addr.c       |   7 +++
 fs/9p/vfs_file.c       | 113 +++++++++++++++++++++++++++++++++++++++++++++++--
 fs/9p/vfs_inode.c      |  17 +++++---
 fs/9p/vfs_inode_dotl.c |   6 +--
 fs/9p/vfs_super.c      |   7 +--
 8 files changed, 146 insertions(+), 16 deletions(-)

diff --git a/fs/9p/v9fs.c b/fs/9p/v9fs.c
index 58e6cbc..1a2b0c8 100644
--- a/fs/9p/v9fs.c
+++ b/fs/9p/v9fs.c
@@ -56,7 +56,7 @@ enum {
 	/* Options that take no arguments */
 	Opt_nodevmap,
 	/* Cache options */
-	Opt_cache_loose, Opt_fscache,
+	Opt_cache_loose, Opt_fscache, Opt_mmap,
 	/* Access options */
 	Opt_access, Opt_posixacl,
 	/* Error token */
@@ -74,6 +74,7 @@ static const match_table_t tokens = {
 	{Opt_cache, "cache=%s"},
 	{Opt_cache_loose, "loose"},
 	{Opt_fscache, "fscache"},
+	{Opt_mmap, "mmap"},
 	{Opt_cachetag, "cachetag=%s"},
 	{Opt_access, "access=%s"},
 	{Opt_posixacl, "posixacl"},
@@ -91,6 +92,9 @@ static int get_cache_mode(char *s)
 	} else if (!strcmp(s, "fscache")) {
 		version = CACHE_FSCACHE;
 		p9_debug(P9_DEBUG_9P, "Cache mode: fscache\n");
+	} else if (!strcmp(s, "mmap")) {
+		version = CACHE_MMAP;
+		p9_debug(P9_DEBUG_9P, "Cache mode: mmap\n");
 	} else if (!strcmp(s, "none")) {
 		version = CACHE_NONE;
 		p9_debug(P9_DEBUG_9P, "Cache mode: none\n");
@@ -220,6 +224,9 @@ static int v9fs_parse_options(struct v9fs_session_info *v9ses, char *opts)
 		case Opt_fscache:
 			v9ses->cache = CACHE_FSCACHE;
 			break;
+		case Opt_mmap:
+			v9ses->cache = CACHE_MMAP;
+			break;
 		case Opt_cachetag:
 #ifdef CONFIG_9P_FSCACHE
 			v9ses->cachetag = match_strdup(&args[0]);
diff --git a/fs/9p/v9fs.h b/fs/9p/v9fs.h
index a8e127c..099c771 100644
--- a/fs/9p/v9fs.h
+++ b/fs/9p/v9fs.h
@@ -64,6 +64,7 @@ enum p9_session_flags {
 
 enum p9_cache_modes {
 	CACHE_NONE,
+	CACHE_MMAP,
 	CACHE_LOOSE,
 	CACHE_FSCACHE,
 };
diff --git a/fs/9p/v9fs_vfs.h b/fs/9p/v9fs_vfs.h
index dc95a25..b83ebfb 100644
--- a/fs/9p/v9fs_vfs.h
+++ b/fs/9p/v9fs_vfs.h
@@ -50,6 +50,8 @@ extern const struct dentry_operations v9fs_dentry_operations;
 extern const struct dentry_operations v9fs_cached_dentry_operations;
 extern const struct file_operations v9fs_cached_file_operations;
 extern const struct file_operations v9fs_cached_file_operations_dotl;
+extern const struct file_operations v9fs_mmap_file_operations;
+extern const struct file_operations v9fs_mmap_file_operations_dotl;
 extern struct kmem_cache *v9fs_inode_cache;
 
 struct inode *v9fs_alloc_inode(struct super_block *sb);
diff --git a/fs/9p/vfs_addr.c b/fs/9p/vfs_addr.c
index 9ff073f..c71e886 100644
--- a/fs/9p/vfs_addr.c
+++ b/fs/9p/vfs_addr.c
@@ -202,6 +202,8 @@ static int v9fs_vfs_writepage(struct page *page, struct writeback_control *wbc)
 {
 	int retval;
 
+	p9_debug(P9_DEBUG_VFS, "page %p\n", page);
+
 	retval = v9fs_vfs_writepage_locked(page);
 	if (retval < 0) {
 		if (retval == -EAGAIN) {
@@ -282,6 +284,9 @@ static int v9fs_write_begin(struct file *filp, struct address_space *mapping,
 	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
 	struct inode *inode = mapping->host;
 
+
+	p9_debug(P9_DEBUG_VFS, "filp %p, mapping %p\n", filp, mapping);
+
 	v9inode = V9FS_I(inode);
 start:
 	page = grab_cache_page_write_begin(mapping, index, flags);
@@ -312,6 +317,8 @@ static int v9fs_write_end(struct file *filp, struct address_space *mapping,
 	loff_t last_pos = pos + copied;
 	struct inode *inode = page->mapping->host;
 
+	p9_debug(P9_DEBUG_VFS, "filp %p, mapping %p\n", filp, mapping);
+
 	if (unlikely(copied < len)) {
 		/*
 		 * zero out the rest of the area
diff --git a/fs/9p/vfs_file.c b/fs/9p/vfs_file.c
index d384a8b..ec904ed 100644
--- a/fs/9p/vfs_file.c
+++ b/fs/9p/vfs_file.c
@@ -45,6 +45,7 @@
 #include "cache.h"
 
 static const struct vm_operations_struct v9fs_file_vm_ops;
+static const struct vm_operations_struct v9fs_mmap_file_vm_ops;
 
 /**
  * v9fs_file_open - open a file (or directory)
@@ -106,7 +107,9 @@ int v9fs_file_open(struct inode *inode, struct file *file)
 	}
 	mutex_unlock(&v9inode->v_mutex);
 #ifdef CONFIG_9P_FSCACHE
-	if (v9ses->cache)
+	/* previous check would also set cookie with CACHE_LOOSE?
+	 * set_cookie does a check if v9inode->fscache anyway... */
+	if (v9ses->cache == CACHE_FSCACHE)
 		v9fs_cache_inode_set_cookie(inode, file);
 #endif
 	return 0;
@@ -583,17 +586,33 @@ int v9fs_file_fsync_dotl(struct file *filp, loff_t start, loff_t end,
 }
 
 static int
-v9fs_file_mmap(struct file *file, struct vm_area_struct *vma)
+v9fs_file_mmap(struct file *filp, struct vm_area_struct *vma)
 {
 	int retval;
 
-	retval = generic_file_mmap(file, vma);
+
+	retval = generic_file_mmap(filp, vma);
 	if (!retval)
 		vma->vm_ops = &v9fs_file_vm_ops;
 
 	return retval;
 }
 
+/* TODO: merge this with the previous function
+ * and set the right vm_ops depending on v9ses->cache */
+static int
+v9fs_mmap_file_mmap(struct file *filp, struct vm_area_struct *vma)
+{
+	int retval;
+
+
+	retval = generic_file_mmap(filp, vma);
+	if (!retval)
+		vma->vm_ops = &v9fs_mmap_file_vm_ops;
+
+	return retval;
+}
+
 static int
 v9fs_vm_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
@@ -662,6 +681,22 @@ v9fs_cached_file_read(struct file *filp, char __user *data, size_t count,
 	return do_sync_read(filp, data, count, offset);
 }
 
+/**
+ * v9fs_mmap_file_read - read from a file
+ * @filp: file pointer to read
+ * @udata: user data buffer to read data into
+ * @count: size of buffer
+ * @offset: offset at which to read data
+ *
+ */
+static ssize_t
+v9fs_mmap_file_read(struct file *filp, char __user *data, size_t count,
+		      loff_t *offset)
+{
+	/* TODO: Check if there are dirty pages */
+	return v9fs_file_read(filp, data, count, offset);
+}
+
 static ssize_t
 v9fs_direct_write(struct file *filp, const char __user * data,
 		  size_t count, loff_t *offsetp)
@@ -732,12 +767,61 @@ v9fs_cached_file_write(struct file *filp, const char __user * data,
 	return do_sync_write(filp, data, count, offset);
 }
 
+
+/**
+ * v9fs_mmap_file_write - write to a file
+ * @filp: file pointer to write
+ * @data: data buffer to write data from
+ * @count: size of buffer
+ * @offset: offset at which to write data
+ *
+ */
+static ssize_t
+v9fs_mmap_file_write(struct file *filp, const char __user *data,
+		       size_t count, loff_t *offset)
+{
+	/* TODO: invalidate mmaps on filp's inode between offset and offset+count */
+	return v9fs_file_write(filp, data, count, offset);
+}
+
+static void v9fs_mmap_vm_close(struct vm_area_struct *vma)
+{
+        struct inode *inode;
+
+	p9_debug(P9_DEBUG_VFS, "9p VMA close, %p, flushing", vma);
+
+	struct writeback_control wbc = {
+		.nr_to_write = LONG_MAX,
+		.sync_mode = WB_SYNC_ALL,
+		.range_start = vma->vm_pgoff * PAGE_SIZE,
+		 /* absolute end, byte at end included */
+		.range_end = vma->vm_pgoff * PAGE_SIZE +
+			(vma->vm_end - vma->vm_start - 1),
+	};
+
+	inode = file_inode(vma->vm_file);
+
+	if (!mapping_cap_writeback_dirty(inode->i_mapping))
+		wbc.nr_to_write = 0;
+
+	might_sleep();
+	sync_inode(inode, &wbc);
+}
+
+
 static const struct vm_operations_struct v9fs_file_vm_ops = {
 	.fault = filemap_fault,
 	.page_mkwrite = v9fs_vm_page_mkwrite,
 	.remap_pages = generic_file_remap_pages,
 };
 
+static const struct vm_operations_struct v9fs_mmap_file_vm_ops = {
+	.close = v9fs_mmap_vm_close,
+	.fault = filemap_fault,
+	.page_mkwrite = v9fs_vm_page_mkwrite,
+	.remap_pages = generic_file_remap_pages,
+};
+
 
 const struct file_operations v9fs_cached_file_operations = {
 	.llseek = generic_file_llseek,
@@ -788,3 +872,26 @@ const struct file_operations v9fs_file_operations_dotl = {
 	.mmap = generic_file_readonly_mmap,
 	.fsync = v9fs_file_fsync_dotl,
 };
+
+const struct file_operations v9fs_mmap_file_operations = {
+	.llseek = generic_file_llseek,
+	.read = v9fs_mmap_file_read,
+	.write = v9fs_mmap_file_write,
+	.open = v9fs_file_open,
+	.release = v9fs_dir_release,
+	.lock = v9fs_file_lock,
+	.mmap = v9fs_mmap_file_mmap,
+	.fsync = v9fs_file_fsync,
+};
+
+const struct file_operations v9fs_mmap_file_operations_dotl = {
+	.llseek = generic_file_llseek,
+	.read = v9fs_mmap_file_read,
+	.write = v9fs_mmap_file_write,
+	.open = v9fs_file_open,
+	.release = v9fs_dir_release,
+	.lock = v9fs_file_lock_dotl,
+	.flock = v9fs_file_flock_dotl,
+	.mmap = v9fs_mmap_file_mmap,
+	.fsync = v9fs_file_fsync_dotl,
+};
diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
index 25b018e..d52179c 100644
--- a/fs/9p/vfs_inode.c
+++ b/fs/9p/vfs_inode.c
@@ -299,15 +299,20 @@ int v9fs_init_inode(struct v9fs_session_info *v9ses,
 	case S_IFREG:
 		if (v9fs_proto_dotl(v9ses)) {
 			inode->i_op = &v9fs_file_inode_operations_dotl;
-			if (v9ses->cache)
+			if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
 				inode->i_fop =
 					&v9fs_cached_file_operations_dotl;
+			else if (v9ses->cache == CACHE_MMAP)
+				inode->i_fop = &v9fs_mmap_file_operations_dotl;
 			else
 				inode->i_fop = &v9fs_file_operations_dotl;
 		} else {
 			inode->i_op = &v9fs_file_inode_operations;
-			if (v9ses->cache)
-				inode->i_fop = &v9fs_cached_file_operations;
+			if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
+				inode->i_fop =
+					&v9fs_cached_file_operations;
+			else if (v9ses->cache == CACHE_MMAP)
+				inode->i_fop = &v9fs_mmap_file_operations;
 			else
 				inode->i_fop = &v9fs_file_operations;
 		}
@@ -816,7 +821,7 @@ struct dentry *v9fs_vfs_lookup(struct inode *dir, struct dentry *dentry,
 	 * unlink. For cached mode create calls request for new
 	 * inode. But with cache disabled, lookup should do this.
 	 */
-	if (v9ses->cache)
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
 		inode = v9fs_get_inode_from_fid(v9ses, fid, dir->i_sb);
 	else
 		inode = v9fs_get_new_inode_from_fid(v9ses, fid, dir->i_sb);
@@ -906,7 +911,7 @@ v9fs_vfs_atomic_open(struct inode *dir, struct dentry *dentry,
 
 	file->private_data = fid;
 #ifdef CONFIG_9P_FSCACHE
-	if (v9ses->cache)
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
 		v9fs_cache_inode_set_cookie(dentry->d_inode, file);
 #endif
 
@@ -1485,7 +1490,7 @@ int v9fs_refresh_inode(struct p9_fid *fid, struct inode *inode)
 	 */
 	i_size = inode->i_size;
 	v9fs_stat2inode(st, inode, inode->i_sb);
-	if (v9ses->cache)
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
 		inode->i_size = i_size;
 	spin_unlock(&inode->i_lock);
 out:
diff --git a/fs/9p/vfs_inode_dotl.c b/fs/9p/vfs_inode_dotl.c
index 53687bb..710d5c6 100644
--- a/fs/9p/vfs_inode_dotl.c
+++ b/fs/9p/vfs_inode_dotl.c
@@ -362,7 +362,7 @@ v9fs_vfs_atomic_open_dotl(struct inode *dir, struct dentry *dentry,
 		goto err_clunk_old_fid;
 	file->private_data = ofid;
 #ifdef CONFIG_9P_FSCACHE
-	if (v9ses->cache)
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
 		v9fs_cache_inode_set_cookie(inode, file);
 #endif
 	*opened |= FILE_CREATED;
@@ -725,7 +725,7 @@ v9fs_vfs_symlink_dotl(struct inode *dir, struct dentry *dentry,
 	}
 
 	v9fs_invalidate_inode_attr(dir);
-	if (v9ses->cache) {
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE) {
 		/* Now walk from the parent so we can get an unopened fid. */
 		fid = p9_client_walk(dfid, 1, &name, 1);
 		if (IS_ERR(fid)) {
@@ -983,7 +983,7 @@ int v9fs_refresh_inode_dotl(struct p9_fid *fid, struct inode *inode)
 	 */
 	i_size = inode->i_size;
 	v9fs_stat2inode_dotl(st, inode);
-	if (v9ses->cache)
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
 		inode->i_size = i_size;
 	spin_unlock(&inode->i_lock);
 out:
diff --git a/fs/9p/vfs_super.c b/fs/9p/vfs_super.c
index 2756dcd..a4dd162 100644
--- a/fs/9p/vfs_super.c
+++ b/fs/9p/vfs_super.c
@@ -144,7 +144,7 @@ static struct dentry *v9fs_mount(struct file_system_type *fs_type, int flags,
 	}
 	v9fs_fill_super(sb, v9ses, flags, data);
 
-	if (v9ses->cache)
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
 		sb->s_d_op = &v9fs_cached_dentry_operations;
 	else
 		sb->s_d_op = &v9fs_dentry_operations;
@@ -282,7 +282,7 @@ static int v9fs_drop_inode(struct inode *inode)
 {
 	struct v9fs_session_info *v9ses;
 	v9ses = v9fs_inode2v9ses(inode);
-	if (v9ses->cache)
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
 		return generic_drop_inode(inode);
 	/*
 	 * in case of non cached mode always drop the
@@ -325,10 +325,11 @@ static int v9fs_write_inode_dotl(struct inode *inode,
 	 * send an fsync request to server irrespective of
 	 * wbc->sync_mode.
 	 */
-	p9_debug(P9_DEBUG_VFS, "%s: inode %p\n", __func__, inode);
 	v9inode = V9FS_I(inode);
+	p9_debug(P9_DEBUG_VFS, "%s: inode %p, writeback_fid %p\n", __func__, inode, v9inode->writeback_fid);
 	if (!v9inode->writeback_fid)
 		return 0;
+
 	ret = p9_client_fsync(v9inode->writeback_fid, 0);
 	if (ret < 0) {
 		__mark_inode_dirty(inode, I_DIRTY_DATASYNC);
-- 
1.8.1.4

[PATCH] 9P: introduction of a new cache=mmap model.

[Dominique Martinet]

 - Add cache=mmap option
 - Make mmap read-write while keeping it as synchronous as possible
 - Build writeback fid on mmap creation if it is writable

Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
---
Changes from RFCv2 to first real version:
 - Fixed things with checkpatch (sorry!)
 - Open writeback fids only on writeable mmaps

It's still probably missing a replacement to v9fs_fscache_wait_on_page_write,
but I can't find any corner case for which this doesn't work...
So I'll just assume it does for now, and will eventually fix that
in a future patch.


Changes from RFCv1 to RFCv2:
 - Changed write_inode_now to sync_inode with the specific region
relating the mmap'd area (I'm honestly not sure about bounds, but it
covers at least the area pointed by the vma_struct. There doesn't seem
to be many functions using sync_inode, should I use do_writeback
directly instead? does it still make sense to check
mapping_cap_writeback_dirty on inode mapping when I'm using sync on a
sub-range?)
 - Fixed one v9ses->cache check that kept inodes around in cache

Missing for offering a real patch:
 - I didn't get any reply on what v9fs_fscache_wait_on_page_write
is called for, so mkwrite might still be wrong given it technically
doesn't wait for anything.
 - I originally wanted to open writeback fids at the same places as
the other cache modems, but it does seem like a waste and will move it
to the mmap creation call; a shame to duplicate code but there really
were many unused fids open because of this
 - More complains/comments :)




Original comment:
I brought up the issue of mmap being read-only with cache=none a bit
ago, and worked on it since.

Here's what this patch does:
 - Add an option cache=mmap (or just mmap, like other caches), nothing
changes for default or other caches.
The following assumes cache=mmap.
 - fills in writeback_fid on open (this could be done in
v9fs_file_mmap since we don't enable buffered write either, but I
wanted to keep the code shared with other caches, so we just have
useless writeback fids most of the time)
 - flush mmap data synchronously on munmap (vma->vm_op->close), this
is because we don't want to use the cache for read, so we need the
modifications to take place immediately. I'm not quite sure why I had
to force it, but it's lost otherwise (with buffered reads, you'd read
from the mmap pages anyway and it wouldn't matter if it's flushed
later - this doesn't really work for this case)


What works:
 - msync(addr, length, MS_SYNC) (MS_SYNC might just be the default
behaviour) does sync correctly;
 - munmap does a sync as well, obviously;
 - no msync/msync with MS_ASYNC will eventually flush when the kernel
decides to.

What doesn't:
 - If you want to read a file after writting in a mmap'd section with
no msync (or msync with MS_ASYNC) and no munmap, you will read what
the servers  knows about -- so the old data. With buffered read,
you'd expect the read to find about the map and use it, we don't.
There is, however, what the documentation says so I don't see this as
a bug. What could probably be done would be to check on read if we
have dirty mapped pages and flush them before reading? I'm not too
sure I like this idea.
 - Likewise, if you write with a map open, the map won't be updated
unless something else invalidates it. I guess we should do that like
the direct write function does.


All in all, while I'm unhappy that I had to use write_inode_now() in
vm_ops->close, I would guess it works for what it is (i.e. an unsafe
feature on a networking filesystem); at least it seems better than
returning ENOTSUPP for my own usage, given read mmap isn't much safer
anyway, and that's why it's an option.


There are a few questions/TODO marks and p9_debug lines that could go
away, but figured it probably makes more sense to leave it there for
an RFC patch.
(Also a few lines over 80 characters I'll fix for the real deal)


Comments more than welcome, thanks!

 fs/9p/v9fs.c           |   9 +++-
 fs/9p/v9fs.h           |   1 +
 fs/9p/v9fs_vfs.h       |   2 +
 fs/9p/vfs_addr.c       |   7 +++
 fs/9p/vfs_file.c       | 142 +++++++++++++++++++++++++++++++++++++++++++++++--
 fs/9p/vfs_inode.c      |  22 +++++---
 fs/9p/vfs_inode_dotl.c |   9 ++--
 fs/9p/vfs_super.c      |   8 +--
 8 files changed, 181 insertions(+), 19 deletions(-)

diff --git a/fs/9p/v9fs.c b/fs/9p/v9fs.c
index 58e6cbc..1a2b0c8 100644
--- a/fs/9p/v9fs.c
+++ b/fs/9p/v9fs.c
@@ -56,7 +56,7 @@ enum {
 	/* Options that take no arguments */
 	Opt_nodevmap,
 	/* Cache options */
-	Opt_cache_loose, Opt_fscache,
+	Opt_cache_loose, Opt_fscache, Opt_mmap,
 	/* Access options */
 	Opt_access, Opt_posixacl,
 	/* Error token */
@@ -74,6 +74,7 @@ static const match_table_t tokens = {
 	{Opt_cache, "cache=%s"},
 	{Opt_cache_loose, "loose"},
 	{Opt_fscache, "fscache"},
+	{Opt_mmap, "mmap"},
 	{Opt_cachetag, "cachetag=%s"},
 	{Opt_access, "access=%s"},
 	{Opt_posixacl, "posixacl"},
@@ -91,6 +92,9 @@ static int get_cache_mode(char *s)
 	} else if (!strcmp(s, "fscache")) {
 		version = CACHE_FSCACHE;
 		p9_debug(P9_DEBUG_9P, "Cache mode: fscache\n");
+	} else if (!strcmp(s, "mmap")) {
+		version = CACHE_MMAP;
+		p9_debug(P9_DEBUG_9P, "Cache mode: mmap\n");
 	} else if (!strcmp(s, "none")) {
 		version = CACHE_NONE;
 		p9_debug(P9_DEBUG_9P, "Cache mode: none\n");
@@ -220,6 +224,9 @@ static int v9fs_parse_options(struct v9fs_session_info *v9ses, char *opts)
 		case Opt_fscache:
 			v9ses->cache = CACHE_FSCACHE;
 			break;
+		case Opt_mmap:
+			v9ses->cache = CACHE_MMAP;
+			break;
 		case Opt_cachetag:
 #ifdef CONFIG_9P_FSCACHE
 			v9ses->cachetag = match_strdup(&args[0]);
diff --git a/fs/9p/v9fs.h b/fs/9p/v9fs.h
index a8e127c..099c771 100644
--- a/fs/9p/v9fs.h
+++ b/fs/9p/v9fs.h
@@ -64,6 +64,7 @@ enum p9_session_flags {
 
 enum p9_cache_modes {
 	CACHE_NONE,
+	CACHE_MMAP,
 	CACHE_LOOSE,
 	CACHE_FSCACHE,
 };
diff --git a/fs/9p/v9fs_vfs.h b/fs/9p/v9fs_vfs.h
index dc95a25..b83ebfb 100644
--- a/fs/9p/v9fs_vfs.h
+++ b/fs/9p/v9fs_vfs.h
@@ -50,6 +50,8 @@ extern const struct dentry_operations v9fs_dentry_operations;
 extern const struct dentry_operations v9fs_cached_dentry_operations;
 extern const struct file_operations v9fs_cached_file_operations;
 extern const struct file_operations v9fs_cached_file_operations_dotl;
+extern const struct file_operations v9fs_mmap_file_operations;
+extern const struct file_operations v9fs_mmap_file_operations_dotl;
 extern struct kmem_cache *v9fs_inode_cache;
 
 struct inode *v9fs_alloc_inode(struct super_block *sb);
diff --git a/fs/9p/vfs_addr.c b/fs/9p/vfs_addr.c
index 9ff073f..c71e886 100644
--- a/fs/9p/vfs_addr.c
+++ b/fs/9p/vfs_addr.c
@@ -202,6 +202,8 @@ static int v9fs_vfs_writepage(struct page *page, struct writeback_control *wbc)
 {
 	int retval;
 
+	p9_debug(P9_DEBUG_VFS, "page %p\n", page);
+
 	retval = v9fs_vfs_writepage_locked(page);
 	if (retval < 0) {
 		if (retval == -EAGAIN) {
@@ -282,6 +284,9 @@ static int v9fs_write_begin(struct file *filp, struct address_space *mapping,
 	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
 	struct inode *inode = mapping->host;
 
+
+	p9_debug(P9_DEBUG_VFS, "filp %p, mapping %p\n", filp, mapping);
+
 	v9inode = V9FS_I(inode);
 start:
 	page = grab_cache_page_write_begin(mapping, index, flags);
@@ -312,6 +317,8 @@ static int v9fs_write_end(struct file *filp, struct address_space *mapping,
 	loff_t last_pos = pos + copied;
 	struct inode *inode = page->mapping->host;
 
+	p9_debug(P9_DEBUG_VFS, "filp %p, mapping %p\n", filp, mapping);
+
 	if (unlikely(copied < len)) {
 		/*
 		 * zero out the rest of the area
diff --git a/fs/9p/vfs_file.c b/fs/9p/vfs_file.c
index d384a8b..8e9c573 100644
--- a/fs/9p/vfs_file.c
+++ b/fs/9p/vfs_file.c
@@ -45,6 +45,7 @@
 #include "cache.h"
 
 static const struct vm_operations_struct v9fs_file_vm_ops;
+static const struct vm_operations_struct v9fs_mmap_file_vm_ops;
 
 /**
  * v9fs_file_open - open a file (or directory)
@@ -87,7 +88,8 @@ int v9fs_file_open(struct inode *inode, struct file *file)
 
 	file->private_data = fid;
 	mutex_lock(&v9inode->v_mutex);
-	if (v9ses->cache && !v9inode->writeback_fid &&
+	if ((v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE) &&
+	    !v9inode->writeback_fid &&
 	    ((file->f_flags & O_ACCMODE) != O_RDONLY)) {
 		/*
 		 * clone a fid and add it to writeback_fid
@@ -106,7 +108,9 @@ int v9fs_file_open(struct inode *inode, struct file *file)
 	}
 	mutex_unlock(&v9inode->v_mutex);
 #ifdef CONFIG_9P_FSCACHE
-	if (v9ses->cache)
+	/* previous check would also set cookie with CACHE_LOOSE?
+	 * set_cookie does a check if v9inode->fscache anyway... */
+	if (v9ses->cache == CACHE_FSCACHE)
 		v9fs_cache_inode_set_cookie(inode, file);
 #endif
 	return 0;
@@ -583,11 +587,12 @@ int v9fs_file_fsync_dotl(struct file *filp, loff_t start, loff_t end,
 }
 
 static int
-v9fs_file_mmap(struct file *file, struct vm_area_struct *vma)
+v9fs_file_mmap(struct file *filp, struct vm_area_struct *vma)
 {
 	int retval;
 
-	retval = generic_file_mmap(file, vma);
+
+	retval = generic_file_mmap(filp, vma);
 	if (!retval)
 		vma->vm_ops = &v9fs_file_vm_ops;
 
@@ -595,6 +600,43 @@ v9fs_file_mmap(struct file *file, struct vm_area_struct *vma)
 }
 
 static int
+v9fs_mmap_file_mmap(struct file *filp, struct vm_area_struct *vma)
+{
+	int retval;
+	struct inode *inode;
+	struct v9fs_inode *v9inode;
+	struct p9_fid *fid;
+
+	inode = file_inode(filp);
+	v9inode = V9FS_I(inode);
+	mutex_lock(&v9inode->v_mutex);
+	if (!v9inode->writeback_fid &&
+	    (vma->vm_flags & VM_WRITE)) {
+		/*
+		 * clone a fid and add it to writeback_fid
+		 * we do it during mmap instead of
+		 * page dirty time via write_begin/page_mkwrite
+		 * because we want write after unlink usecase
+		 * to work.
+		 */
+		fid = v9fs_writeback_fid(filp->f_path.dentry);
+		if (IS_ERR(fid)) {
+			retval = PTR_ERR(fid);
+			mutex_unlock(&v9inode->v_mutex);
+			return retval;
+		}
+		v9inode->writeback_fid = (void *) fid;
+	}
+	mutex_unlock(&v9inode->v_mutex);
+
+	retval = generic_file_mmap(filp, vma);
+	if (!retval)
+		vma->vm_ops = &v9fs_mmap_file_vm_ops;
+
+	return retval;
+}
+
+static int
 v9fs_vm_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
 	struct v9fs_inode *v9inode;
@@ -662,6 +704,22 @@ v9fs_cached_file_read(struct file *filp, char __user *data, size_t count,
 	return do_sync_read(filp, data, count, offset);
 }
 
+/**
+ * v9fs_mmap_file_read - read from a file
+ * @filp: file pointer to read
+ * @udata: user data buffer to read data into
+ * @count: size of buffer
+ * @offset: offset at which to read data
+ *
+ */
+static ssize_t
+v9fs_mmap_file_read(struct file *filp, char __user *data, size_t count,
+		      loff_t *offset)
+{
+	/* TODO: Check if there are dirty pages */
+	return v9fs_file_read(filp, data, count, offset);
+}
+
 static ssize_t
 v9fs_direct_write(struct file *filp, const char __user * data,
 		  size_t count, loff_t *offsetp)
@@ -732,12 +790,65 @@ v9fs_cached_file_write(struct file *filp, const char __user * data,
 	return do_sync_write(filp, data, count, offset);
 }
 
+
+/**
+ * v9fs_mmap_file_write - write to a file
+ * @filp: file pointer to write
+ * @data: data buffer to write data from
+ * @count: size of buffer
+ * @offset: offset at which to write data
+ *
+ */
+static ssize_t
+v9fs_mmap_file_write(struct file *filp, const char __user *data,
+		       size_t count, loff_t *offset)
+{
+	/*
+	 * TODO: invalidate mmaps on filp's inode between
+	 * offset and offset+count
+	 */
+	return v9fs_file_write(filp, data, count, offset);
+}
+
+static void v9fs_mmap_vm_close(struct vm_area_struct *vma)
+{
+	struct inode *inode;
+
+	struct writeback_control wbc = {
+		.nr_to_write = LONG_MAX,
+		.sync_mode = WB_SYNC_ALL,
+		.range_start = vma->vm_pgoff * PAGE_SIZE,
+		 /* absolute end, byte at end included */
+		.range_end = vma->vm_pgoff * PAGE_SIZE +
+			(vma->vm_end - vma->vm_start - 1),
+	};
+
+
+	p9_debug(P9_DEBUG_VFS, "9p VMA close, %p, flushing", vma);
+
+	inode = file_inode(vma->vm_file);
+
+	if (!mapping_cap_writeback_dirty(inode->i_mapping))
+		wbc.nr_to_write = 0;
+
+	might_sleep();
+	sync_inode(inode, &wbc);
+}
+
+
 static const struct vm_operations_struct v9fs_file_vm_ops = {
 	.fault = filemap_fault,
 	.page_mkwrite = v9fs_vm_page_mkwrite,
 	.remap_pages = generic_file_remap_pages,
 };
 
+static const struct vm_operations_struct v9fs_mmap_file_vm_ops = {
+	.close = v9fs_mmap_vm_close,
+	.fault = filemap_fault,
+	.page_mkwrite = v9fs_vm_page_mkwrite,
+	.remap_pages = generic_file_remap_pages,
+};
+
 
 const struct file_operations v9fs_cached_file_operations = {
 	.llseek = generic_file_llseek,
@@ -788,3 +899,26 @@ const struct file_operations v9fs_file_operations_dotl = {
 	.mmap = generic_file_readonly_mmap,
 	.fsync = v9fs_file_fsync_dotl,
 };
+
+const struct file_operations v9fs_mmap_file_operations = {
+	.llseek = generic_file_llseek,
+	.read = v9fs_mmap_file_read,
+	.write = v9fs_mmap_file_write,
+	.open = v9fs_file_open,
+	.release = v9fs_dir_release,
+	.lock = v9fs_file_lock,
+	.mmap = v9fs_mmap_file_mmap,
+	.fsync = v9fs_file_fsync,
+};
+
+const struct file_operations v9fs_mmap_file_operations_dotl = {
+	.llseek = generic_file_llseek,
+	.read = v9fs_mmap_file_read,
+	.write = v9fs_mmap_file_write,
+	.open = v9fs_file_open,
+	.release = v9fs_dir_release,
+	.lock = v9fs_file_lock_dotl,
+	.flock = v9fs_file_flock_dotl,
+	.mmap = v9fs_mmap_file_mmap,
+	.fsync = v9fs_file_fsync_dotl,
+};
diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
index 25b018e..eb74047c 100644
--- a/fs/9p/vfs_inode.c
+++ b/fs/9p/vfs_inode.c
@@ -299,15 +299,22 @@ int v9fs_init_inode(struct v9fs_session_info *v9ses,
 	case S_IFREG:
 		if (v9fs_proto_dotl(v9ses)) {
 			inode->i_op = &v9fs_file_inode_operations_dotl;
-			if (v9ses->cache)
+			if (v9ses->cache == CACHE_LOOSE ||
+			    v9ses->cache == CACHE_FSCACHE)
 				inode->i_fop =
 					&v9fs_cached_file_operations_dotl;
+			else if (v9ses->cache == CACHE_MMAP)
+				inode->i_fop = &v9fs_mmap_file_operations_dotl;
 			else
 				inode->i_fop = &v9fs_file_operations_dotl;
 		} else {
 			inode->i_op = &v9fs_file_inode_operations;
-			if (v9ses->cache)
-				inode->i_fop = &v9fs_cached_file_operations;
+			if (v9ses->cache == CACHE_LOOSE ||
+			    v9ses->cache == CACHE_FSCACHE)
+				inode->i_fop =
+					&v9fs_cached_file_operations;
+			else if (v9ses->cache == CACHE_MMAP)
+				inode->i_fop = &v9fs_mmap_file_operations;
 			else
 				inode->i_fop = &v9fs_file_operations;
 		}
@@ -816,7 +823,7 @@ struct dentry *v9fs_vfs_lookup(struct inode *dir, struct dentry *dentry,
 	 * unlink. For cached mode create calls request for new
 	 * inode. But with cache disabled, lookup should do this.
 	 */
-	if (v9ses->cache)
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
 		inode = v9fs_get_inode_from_fid(v9ses, fid, dir->i_sb);
 	else
 		inode = v9fs_get_new_inode_from_fid(v9ses, fid, dir->i_sb);
@@ -882,7 +889,8 @@ v9fs_vfs_atomic_open(struct inode *dir, struct dentry *dentry,
 	v9fs_invalidate_inode_attr(dir);
 	v9inode = V9FS_I(dentry->d_inode);
 	mutex_lock(&v9inode->v_mutex);
-	if (v9ses->cache && !v9inode->writeback_fid &&
+	if ((v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE) &&
+	    !v9inode->writeback_fid &&
 	    ((flags & O_ACCMODE) != O_RDONLY)) {
 		/*
 		 * clone a fid and add it to writeback_fid
@@ -906,7 +914,7 @@ v9fs_vfs_atomic_open(struct inode *dir, struct dentry *dentry,
 
 	file->private_data = fid;
 #ifdef CONFIG_9P_FSCACHE
-	if (v9ses->cache)
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
 		v9fs_cache_inode_set_cookie(dentry->d_inode, file);
 #endif
 
@@ -1485,7 +1493,7 @@ int v9fs_refresh_inode(struct p9_fid *fid, struct inode *inode)
 	 */
 	i_size = inode->i_size;
 	v9fs_stat2inode(st, inode, inode->i_sb);
-	if (v9ses->cache)
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
 		inode->i_size = i_size;
 	spin_unlock(&inode->i_lock);
 out:
diff --git a/fs/9p/vfs_inode_dotl.c b/fs/9p/vfs_inode_dotl.c
index 53687bb..e48c77b 100644
--- a/fs/9p/vfs_inode_dotl.c
+++ b/fs/9p/vfs_inode_dotl.c
@@ -338,7 +338,8 @@ v9fs_vfs_atomic_open_dotl(struct inode *dir, struct dentry *dentry,
 
 	v9inode = V9FS_I(inode);
 	mutex_lock(&v9inode->v_mutex);
-	if (v9ses->cache && !v9inode->writeback_fid &&
+	if ((v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE) &&
+	    !v9inode->writeback_fid &&
 	    ((flags & O_ACCMODE) != O_RDONLY)) {
 		/*
 		 * clone a fid and add it to writeback_fid
@@ -362,7 +363,7 @@ v9fs_vfs_atomic_open_dotl(struct inode *dir, struct dentry *dentry,
 		goto err_clunk_old_fid;
 	file->private_data = ofid;
 #ifdef CONFIG_9P_FSCACHE
-	if (v9ses->cache)
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
 		v9fs_cache_inode_set_cookie(inode, file);
 #endif
 	*opened |= FILE_CREATED;
@@ -725,7 +726,7 @@ v9fs_vfs_symlink_dotl(struct inode *dir, struct dentry *dentry,
 	}
 
 	v9fs_invalidate_inode_attr(dir);
-	if (v9ses->cache) {
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE) {
 		/* Now walk from the parent so we can get an unopened fid. */
 		fid = p9_client_walk(dfid, 1, &name, 1);
 		if (IS_ERR(fid)) {
@@ -983,7 +984,7 @@ int v9fs_refresh_inode_dotl(struct p9_fid *fid, struct inode *inode)
 	 */
 	i_size = inode->i_size;
 	v9fs_stat2inode_dotl(st, inode);
-	if (v9ses->cache)
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
 		inode->i_size = i_size;
 	spin_unlock(&inode->i_lock);
 out:
diff --git a/fs/9p/vfs_super.c b/fs/9p/vfs_super.c
index 2756dcd..0afd038 100644
--- a/fs/9p/vfs_super.c
+++ b/fs/9p/vfs_super.c
@@ -144,7 +144,7 @@ static struct dentry *v9fs_mount(struct file_system_type *fs_type, int flags,
 	}
 	v9fs_fill_super(sb, v9ses, flags, data);
 
-	if (v9ses->cache)
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
 		sb->s_d_op = &v9fs_cached_dentry_operations;
 	else
 		sb->s_d_op = &v9fs_dentry_operations;
@@ -282,7 +282,7 @@ static int v9fs_drop_inode(struct inode *inode)
 {
 	struct v9fs_session_info *v9ses;
 	v9ses = v9fs_inode2v9ses(inode);
-	if (v9ses->cache)
+	if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
 		return generic_drop_inode(inode);
 	/*
 	 * in case of non cached mode always drop the
@@ -325,10 +325,12 @@ static int v9fs_write_inode_dotl(struct inode *inode,
 	 * send an fsync request to server irrespective of
 	 * wbc->sync_mode.
 	 */
-	p9_debug(P9_DEBUG_VFS, "%s: inode %p\n", __func__, inode);
 	v9inode = V9FS_I(inode);
+	p9_debug(P9_DEBUG_VFS, "%s: inode %p, writeback_fid %p\n",
+		 __func__, inode, v9inode->writeback_fid);
 	if (!v9inode->writeback_fid)
 		return 0;
+
 	ret = p9_client_fsync(v9inode->writeback_fid, 0);
 	if (ret < 0) {
 		__mark_inode_dirty(inode, I_DIRTY_DATASYNC);
-- 
1.8.1.4