[PATCH][RESEND] vfs: Make __d_materialise_dentry() set the materialised dentry name correctly

[PATCH][RESEND] vfs: Make __d_materialise_dentry() set the materialised dentry name correctly

[Yan, Zheng]

From: David Howells <dhowells@redhat.com>

Make __d_materialise_dentry() set the materialised dentry name correctly by
flipping the arguments to switch_names().

switch_names() is lazy: if both names are internal to their dentries, it'll
overwrite that of the first dentry with that of the second, and won't update
that of the second.

In the case of __d_materialise_dentry(), the second is an already extant
anonymous dentry that we want to insert into the tree in place of the dentry we
just looked up[*].  However, the dentry we just looked up carries the name we
actually want to use.

[*] This is used by NFS to join a mount of a subtree into a mount of a tree
nearer the root when the two meet, where both mounts share a superblock and
thus a set of dentries.

Signed-off-by: David Howells <dhowells@redhat.com>
---
 fs/dcache.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 265e0ce..ff779d4 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2698,7 +2698,7 @@ static void __d_materialise_dentry(struct dentry *dentry, struct dentry *anon)
 
 	dparent = dentry->d_parent;
 
-	switch_names(dentry, anon);
+	switch_names(anon, dentry);
 	swap(dentry->d_name.hash, anon->d_name.hash);
 
 	dentry->d_parent = dentry;
-- 
1.8.5.3

Re: [PATCH][RESEND] vfs: Make __d_materialise_dentry() set the materialised dentry name correctly

[Trond Myklebust]

On Mar 6, 2014, at 9:16, Yan, Zheng <zheng.z.yan@intel.com> wrote:

> From: David Howells <dhowells@redhat.com>
> 
> Make __d_materialise_dentry() set the materialised dentry name correctly by
> flipping the arguments to switch_names().
> 
> switch_names() is lazy: if both names are internal to their dentries, it'll
> overwrite that of the first dentry with that of the second, and won't update
> that of the second.
> 
> In the case of __d_materialise_dentry(), the second is an already extant
> anonymous dentry that we want to insert into the tree in place of the dentry we
> just looked up[*].  However, the dentry we just looked up carries the name we
> actually want to use.
> 
> [*] This is used by NFS to join a mount of a subtree into a mount of a tree
> nearer the root when the two meet, where both mounts share a superblock and
> thus a set of dentries.
> 
> Signed-off-by: David Howells <dhowells@redhat.com>
> ---
> fs/dcache.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/dcache.c b/fs/dcache.c
> index 265e0ce..ff779d4 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -2698,7 +2698,7 @@ static void __d_materialise_dentry(struct dentry *dentry, struct dentry *anon)
> 
> 	dparent = dentry->d_parent;
> 
> -	switch_names(dentry, anon);
> +	switch_names(anon, dentry);
> 	swap(dentry->d_name.hash, anon->d_name.hash);
> 
> 	dentry->d_parent = dentry;

Well spotted...

We ought to better document the fact that ’switch_names’ is asymmetrical. Perhaps change it to ‘update_target_name’, and then switch the argument names so that the ’target’ really is the thing that gets updated?

_________________________________
Trond Myklebust
Linux NFS client maintainer, PrimaryData
trond.myklebust@primarydata.com

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Re: [PATCH][RESEND] vfs: Make __d_materialise_dentry() set the materialised dentry name correctly

[J. Bruce Fields]

On Thu, Mar 06, 2014 at 09:35:01AM -0500, Trond Myklebust wrote:
> 
> On Mar 6, 2014, at 9:16, Yan, Zheng <zheng.z.yan@intel.com> wrote:
> 
> > From: David Howells <dhowells@redhat.com>
> > 
> > Make __d_materialise_dentry() set the materialised dentry name correctly by
> > flipping the arguments to switch_names().
> > 
> > switch_names() is lazy: if both names are internal to their dentries, it'll
> > overwrite that of the first dentry with that of the second, and won't update
> > that of the second.
> > 
> > In the case of __d_materialise_dentry(), the second is an already extant
> > anonymous dentry that we want to insert into the tree in place of the dentry we
> > just looked up[*].  However, the dentry we just looked up carries the name we
> > actually want to use.
> > 
> > [*] This is used by NFS to join a mount of a subtree into a mount of a tree
> > nearer the root when the two meet, where both mounts share a superblock and
> > thus a set of dentries.
> > 
> > Signed-off-by: David Howells <dhowells@redhat.com>
> > ---
> > fs/dcache.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/fs/dcache.c b/fs/dcache.c
> > index 265e0ce..ff779d4 100644
> > --- a/fs/dcache.c
> > +++ b/fs/dcache.c
> > @@ -2698,7 +2698,7 @@ static void __d_materialise_dentry(struct dentry *dentry, struct dentry *anon)
> > 
> > 	dparent = dentry->d_parent;
> > 
> > -	switch_names(dentry, anon);
> > +	switch_names(anon, dentry);
> > 	swap(dentry->d_name.hash, anon->d_name.hash);
> > 
> > 	dentry->d_parent = dentry;
> 
> Well spotted...
> 
> We ought to better document the fact that ’switch_names’ is asymmetrical. Perhaps change it to ‘update_target_name’, and then switch the argument names so that the ’target’ really is the thing that gets updated?

Probably not worth it if Miklos's RENAME_EXCHANGE operation is making it
symmetrical soon anyway?:

	http://mid.gmane.org/<1380643239-16060-4-git-send-email-miklos@szeredi.hu>

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Re: [PATCH][RESEND] vfs: Make __d_materialise_dentry() set the materialised dentry name correctly

[J. Bruce Fields]

On Fri, Mar 07, 2014 at 01:55:52PM -0500, J. Bruce Fields wrote:
> On Thu, Mar 06, 2014 at 09:35:01AM -0500, Trond Myklebust wrote:
> > 
> > On Mar 6, 2014, at 9:16, Yan, Zheng <zheng.z.yan-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org> wrote:
> > 
> > > From: David Howells <dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> > > 
> > > Make __d_materialise_dentry() set the materialised dentry name correctly by
> > > flipping the arguments to switch_names().
> > > 
> > > switch_names() is lazy: if both names are internal to their dentries, it'll
> > > overwrite that of the first dentry with that of the second, and won't update
> > > that of the second.
> > > 
> > > In the case of __d_materialise_dentry(), the second is an already extant
> > > anonymous dentry that we want to insert into the tree in place of the dentry we
> > > just looked up[*].  However, the dentry we just looked up carries the name we
> > > actually want to use.
> > > 
> > > [*] This is used by NFS to join a mount of a subtree into a mount of a tree
> > > nearer the root when the two meet, where both mounts share a superblock and
> > > thus a set of dentries.
> > > 
> > > Signed-off-by: David Howells <dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> > > ---
> > > fs/dcache.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/fs/dcache.c b/fs/dcache.c
> > > index 265e0ce..ff779d4 100644
> > > --- a/fs/dcache.c
> > > +++ b/fs/dcache.c
> > > @@ -2698,7 +2698,7 @@ static void __d_materialise_dentry(struct dentry *dentry, struct dentry *anon)
> > > 
> > > 	dparent = dentry->d_parent;
> > > 
> > > -	switch_names(dentry, anon);
> > > +	switch_names(anon, dentry);
> > > 	swap(dentry->d_name.hash, anon->d_name.hash);
> > > 
> > > 	dentry->d_parent = dentry;
> > 
> > Well spotted...
> > 
> > We ought to better document the fact that ’switch_names’ is asymmetrical. Perhaps change it to ‘update_target_name’, and then switch the argument names so that the ’target’ really is the thing that gets updated?
> 
> Probably not worth it if Miklos's RENAME_EXCHANGE operation is making it
> symmetrical soon anyway?:
> 
> 	http://mid.gmane.org/<1380643239-16060-4-git-send-email-miklos@szeredi.hu>

To clarify: I mean, the suggested cleanup may not be worth it.  The
__d_materialise_dentry bugfix of course is.

(What I wonder about is the duplication between this and __d_move.  Is
there any way to make d_materialise_unique a special case of d_move?)

--b.
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Re: [PATCH][RESEND] vfs: Make __d_materialise_dentry() set the materialised dentry name correctly

[Yan, Zheng]

Hi Al,

Could you include this in 3.15

Regards
Yan, Zheng

On 03/06/2014 10:35 PM, Trond Myklebust wrote:
> 
> On Mar 6, 2014, at 9:16, Yan, Zheng <zheng.z.yan@intel.com> wrote:
> 
>> From: David Howells <dhowells@redhat.com>
>>
>> Make __d_materialise_dentry() set the materialised dentry name correctly by
>> flipping the arguments to switch_names().
>>
>> switch_names() is lazy: if both names are internal to their dentries, it'll
>> overwrite that of the first dentry with that of the second, and won't update
>> that of the second.
>>
>> In the case of __d_materialise_dentry(), the second is an already extant
>> anonymous dentry that we want to insert into the tree in place of the dentry we
>> just looked up[*].  However, the dentry we just looked up carries the name we
>> actually want to use.
>>
>> [*] This is used by NFS to join a mount of a subtree into a mount of a tree
>> nearer the root when the two meet, where both mounts share a superblock and
>> thus a set of dentries.
>>
>> Signed-off-by: David Howells <dhowells@redhat.com>
>> ---
>> fs/dcache.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/dcache.c b/fs/dcache.c
>> index 265e0ce..ff779d4 100644
>> --- a/fs/dcache.c
>> +++ b/fs/dcache.c
>> @@ -2698,7 +2698,7 @@ static void __d_materialise_dentry(struct dentry *dentry, struct dentry *anon)
>>
>> 	dparent = dentry->d_parent;
>>
>> -	switch_names(dentry, anon);
>> +	switch_names(anon, dentry);
>> 	swap(dentry->d_name.hash, anon->d_name.hash);
>>
>> 	dentry->d_parent = dentry;
> 
> Well spotted...
> 
> We ought to better document the fact that ’switch_names’ is asymmetrical. Perhaps change it to ‘update_target_name’, and then switch the argument names so that the ’target’ really is the thing that gets updated?
> 
> _________________________________
> Trond Myklebust
> Linux NFS client maintainer, PrimaryData
> trond.myklebust@primarydata.com
> 

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Re: [PATCH][RESEND] vfs: Make __d_materialise_dentry() set the materialised dentry name correctly

[Sage Weil]

Hi Al,

Can this go to Linus via your tree?

Thanks!
sage


On Mon, 31 Mar 2014, Yan, Zheng wrote:

> Hi Al,
> 
> Could you include this in 3.15
> 
> Regards
> Yan, Zheng
> 
> On 03/06/2014 10:35 PM, Trond Myklebust wrote:
> > 
> > On Mar 6, 2014, at 9:16, Yan, Zheng <zheng.z.yan-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org> wrote:
> > 
> >> From: David Howells <dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> >>
> >> Make __d_materialise_dentry() set the materialised dentry name correctly by
> >> flipping the arguments to switch_names().
> >>
> >> switch_names() is lazy: if both names are internal to their dentries, it'll
> >> overwrite that of the first dentry with that of the second, and won't update
> >> that of the second.
> >>
> >> In the case of __d_materialise_dentry(), the second is an already extant
> >> anonymous dentry that we want to insert into the tree in place of the dentry we
> >> just looked up[*].  However, the dentry we just looked up carries the name we
> >> actually want to use.
> >>
> >> [*] This is used by NFS to join a mount of a subtree into a mount of a tree
> >> nearer the root when the two meet, where both mounts share a superblock and
> >> thus a set of dentries.
> >>
> >> Signed-off-by: David Howells <dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> >> ---
> >> fs/dcache.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/fs/dcache.c b/fs/dcache.c
> >> index 265e0ce..ff779d4 100644
> >> --- a/fs/dcache.c
> >> +++ b/fs/dcache.c
> >> @@ -2698,7 +2698,7 @@ static void __d_materialise_dentry(struct dentry *dentry, struct dentry *anon)
> >>
> >> 	dparent = dentry->d_parent;
> >>
> >> -	switch_names(dentry, anon);
> >> +	switch_names(anon, dentry);
> >> 	swap(dentry->d_name.hash, anon->d_name.hash);
> >>
> >> 	dentry->d_parent = dentry;
> > 
> > Well spotted...
> > 
> > We ought to better document the fact that ?switch_names? is asymmetrical. Perhaps change it to ?update_target_name?, and then switch the argument names so that the ?target? really is the thing that gets updated?
> > 
> > _________________________________
> > Trond Myklebust
> > Linux NFS client maintainer, PrimaryData
> > trond.myklebust-7I+n7zu2hftEKMMhf/gKZA@public.gmane.org
> > 
> 
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> 
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Re: [PATCH][RESEND] vfs: Make __d_materialise_dentry() set the materialised dentry name correctly

[J. Bruce Fields]

On Mon, Apr 07, 2014 at 06:56:28AM -0700, Sage Weil wrote:
> Hi Al,
> 
> Can this go to Linus via your tree?

I believe this has been fixed by
da1ce0670c14d8380e423a3239e562a1dc15fa9e "vfs: add cross-rename".

Though probably the patch should still go in, possibly with a changelog
update.  We want it for stable kernels if nothing else.

--b.

> 
> Thanks!
> sage
> 
> 
> On Mon, 31 Mar 2014, Yan, Zheng wrote:
> 
> > Hi Al,
> > 
> > Could you include this in 3.15
> > 
> > Regards
> > Yan, Zheng
> > 
> > On 03/06/2014 10:35 PM, Trond Myklebust wrote:
> > > 
> > > On Mar 6, 2014, at 9:16, Yan, Zheng <zheng.z.yan@intel.com> wrote:
> > > 
> > >> From: David Howells <dhowells@redhat.com>
> > >>
> > >> Make __d_materialise_dentry() set the materialised dentry name correctly by
> > >> flipping the arguments to switch_names().
> > >>
> > >> switch_names() is lazy: if both names are internal to their dentries, it'll
> > >> overwrite that of the first dentry with that of the second, and won't update
> > >> that of the second.
> > >>
> > >> In the case of __d_materialise_dentry(), the second is an already extant
> > >> anonymous dentry that we want to insert into the tree in place of the dentry we
> > >> just looked up[*].  However, the dentry we just looked up carries the name we
> > >> actually want to use.
> > >>
> > >> [*] This is used by NFS to join a mount of a subtree into a mount of a tree
> > >> nearer the root when the two meet, where both mounts share a superblock and
> > >> thus a set of dentries.
> > >>
> > >> Signed-off-by: David Howells <dhowells@redhat.com>
> > >> ---
> > >> fs/dcache.c | 2 +-
> > >> 1 file changed, 1 insertion(+), 1 deletion(-)
> > >>
> > >> diff --git a/fs/dcache.c b/fs/dcache.c
> > >> index 265e0ce..ff779d4 100644
> > >> --- a/fs/dcache.c
> > >> +++ b/fs/dcache.c
> > >> @@ -2698,7 +2698,7 @@ static void __d_materialise_dentry(struct dentry *dentry, struct dentry *anon)
> > >>
> > >> 	dparent = dentry->d_parent;
> > >>
> > >> -	switch_names(dentry, anon);
> > >> +	switch_names(anon, dentry);
> > >> 	swap(dentry->d_name.hash, anon->d_name.hash);
> > >>
> > >> 	dentry->d_parent = dentry;
> > > 
> > > Well spotted...
> > > 
> > > We ought to better document the fact that ?switch_names? is asymmetrical. Perhaps change it to ?update_target_name?, and then switch the argument names so that the ?target? really is the thing that gets updated?
> > > 
> > > _________________________________
> > > Trond Myklebust
> > > Linux NFS client maintainer, PrimaryData
> > > trond.myklebust@primarydata.com
> > > 
> > 
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> > 
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