Re: [RFC] sane access to per-fs metadata (was Re: [PATCH] Documentation/ioctl-number.txt)

[Tommi Virtanen]

[EMAIL PROTECTED] (Chip Salzenberg) writes:

> AFAIK, Alex Viro's idea of bindable namespaces provides effective
> transaction support *ONLY* if there are per-process bindings.  With
> per-process bindings, each client that opens a connection does so
> through a distinct binding; when that client's responses go back
> through the same binding, only that client can see them.

Not really. We can both open /proc/partitions, read one char at a
time, and the kernel won't confuse our read positions. Different
file opens create different instances of state. See struct file,
void *private_data for how to store arbitrary data.

-- 
tv@{{hq.yok.utu,havoc,gaeshido}.fi,{debian,wanderer}.org,stonesoft.com}
unix, linux, debian, networks, security, | First snow, then silence.
kernel, TCP/IP, C, perl, free software,  | This thousand dollar screen dies
mail, www, sw devel, unix admin, hacks.  | so beautifully.
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Re: [RFC] sane access to per-fs metadata (was Re: [PATCH] Documentation/ioctl-number.txt)

[Tommi Virtanen]

[EMAIL PROTECTED] (Chip Salzenberg) writes:

 AFAIK, Alex Viro's idea of bindable namespaces provides effective
 transaction support *ONLY* if there are per-process bindings.  With
 per-process bindings, each client that opens a connection does so
 through a distinct binding; when that client's responses go back
 through the same binding, only that client can see them.

Not really. We can both open /proc/partitions, read one char at a
time, and the kernel won't confuse our read positions. Different
file opens create different instances of state. See struct file,
void *private_data for how to store arbitrary data.

-- 
tv@{{hq.yok.utu,havoc,gaeshido}.fi,{debian,wanderer}.org,stonesoft.com}
unix, linux, debian, networks, security, | First snow, then silence.
kernel, TCP/IP, C, perl, free software,  | This thousand dollar screen dies
mail, www, sw devel, unix admin, hacks.  | so beautifully.
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Re: [RFC] sane access to per-fs metadata (was Re: [PATCH] Documentation/ioctl-number.txt)

[Chip Salzenberg]

According to [EMAIL PROTECTED]:
>[EMAIL PROTECTED] (Chip Salzenberg) wrote:
>>Why not have a kernel thread and use standard RPC techniques like
>>sockets?  Then you'd not have to invent anything unimportant like
>>Yet Another IPC Technique.
>
>kerneld (kmod's late unlamented predecessor) used to use Unix sockets
>to communicate from the kernel to the daemon.  It forced everybody to
>link Unix sockets into the kernel but there are some people out there
>who want to use it as a module.  Also the kernel code for communicating
>with kerneld was "unpleasant", see ipc/msg.c in a 2.0 kernel.

I see.

On the other hand, file-style (e.g. /proc-style) access works in Plan9
at least inpart because each client makes his own connection to the
server.  Thus, the question of how clients know which response is for
them is trivially solved.  ('Server' would in this case be the JFS
kernel thread.)

Sockets are apparently not the right way to go about getting
transaction support for kernel threads.

AFAIK, Alex Viro's idea of bindable namespaces provides effective
transaction support *ONLY* if there are per-process bindings.  With
per-process bindings, each client that opens a connection does so
through a distinct binding; when that client's responses go back
through the same binding, only that client can see them.

I hope that Alex's namespaces patch, implementing per-process
bindings, goes into the official kernel Real Soon Now.
-- 
Chip Salzenberg  - a.k.a. - <[EMAIL PROTECTED]>
 "We have no fuel on board, plus or minus 8 kilograms."  -- NEAR tech
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Re: [RFC] sane access to per-fs metadata (was Re: [PATCH] Documentation/ioctl-number.txt)

[Chip Salzenberg]

According to [EMAIL PROTECTED]:
[EMAIL PROTECTED] (Chip Salzenberg) wrote:
Why not have a kernel thread and use standard RPC techniques like
sockets?  Then you'd not have to invent anything unimportant like
Yet Another IPC Technique.

kerneld (kmod's late unlamented predecessor) used to use Unix sockets
to communicate from the kernel to the daemon.  It forced everybody to
link Unix sockets into the kernel but there are some people out there
who want to use it as a module.  Also the kernel code for communicating
with kerneld was "unpleasant", see ipc/msg.c in a 2.0 kernel.

I see.

On the other hand, file-style (e.g. /proc-style) access works in Plan9
at least inpart because each client makes his own connection to the
server.  Thus, the question of how clients know which response is for
them is trivially solved.  ('Server' would in this case be the JFS
kernel thread.)

Sockets are apparently not the right way to go about getting
transaction support for kernel threads.

AFAIK, Alex Viro's idea of bindable namespaces provides effective
transaction support *ONLY* if there are per-process bindings.  With
per-process bindings, each client that opens a connection does so
through a distinct binding; when that client's responses go back
through the same binding, only that client can see them.

I hope that Alex's namespaces patch, implementing per-process
bindings, goes into the official kernel Real Soon Now.
-- 
Chip Salzenberg  - a.k.a. - [EMAIL PROTECTED]
 "We have no fuel on board, plus or minus 8 kilograms."  -- NEAR tech
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Re: [RFC] sane access to per-fs metadata (was Re: [PATCH] Documentation/ioctl-number.txt)

[Keith Owens]

On Sun, 01 Apr 2001 01:01:59 -0800, 
[EMAIL PROTECTED] (Chip Salzenberg) wrote:
>In article  you write:
>Why not have a kernel thread and use standard RPC techniques like
>sockets?  Then you'd not have to invent anything unimportant like
>Yet Another IPC Technique.

kerneld (kmod's late unlamented predecessor) used to use Unix sockets
to communicate from the kernel to the daemon.  It forced everybody to
link Unix sockets into the kernel but there are some people out there
who want to use it as a module.  Also the kernel code for communicating
with kerneld was "unpleasant", see ipc/msg.c in a 2.0 kernel.

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Re: [RFC] sane access to per-fs metadata (was Re: [PATCH] Documentation/ioctl-number.txt)

[Chip Salzenberg]

In article  you write:
>With ioctl, I can easily match a response of any kind to a request.  I can 
>even return an English text message if I want to be friendly.

But ioctl requires allocation of numbers.  Ugly and hard to scale.

Alex Viro's idea is cleaner, but still requires a fair amount of
coding even for simple interfaces.

Why not have a kernel thread and use standard RPC techniques like
sockets?  Then you'd not have to invent anything unimportant like
Yet Another IPC Technique.
-- 
Chip Salzenberg  - a.k.a. - <[EMAIL PROTECTED]>
 "We have no fuel on board, plus or minus 8 kilograms."  -- NEAR tech
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Re: [RFC] sane access to per-fs metadata (was Re: [PATCH] Documentation/ioctl-number.txt)

[Chip Salzenberg]

In article OF791BBBC5.E3FCBEEE-ON87256A18.005BA3B7@LocalDomain you write:
With ioctl, I can easily match a response of any kind to a request.  I can 
even return an English text message if I want to be friendly.

But ioctl requires allocation of numbers.  Ugly and hard to scale.

Alex Viro's idea is cleaner, but still requires a fair amount of
coding even for simple interfaces.

Why not have a kernel thread and use standard RPC techniques like
sockets?  Then you'd not have to invent anything unimportant like
Yet Another IPC Technique.
-- 
Chip Salzenberg  - a.k.a. - [EMAIL PROTECTED]
 "We have no fuel on board, plus or minus 8 kilograms."  -- NEAR tech
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Re: [RFC] sane access to per-fs metadata (was Re: [PATCH] Documentation/ioctl-number.txt)

[Keith Owens]

On Sun, 01 Apr 2001 01:01:59 -0800, 
[EMAIL PROTECTED] (Chip Salzenberg) wrote:
In article OF791BBBC5.E3FCBEEE-ON87256A18.005BA3B7@LocalDomain you write:
Why not have a kernel thread and use standard RPC techniques like
sockets?  Then you'd not have to invent anything unimportant like
Yet Another IPC Technique.

kerneld (kmod's late unlamented predecessor) used to use Unix sockets
to communicate from the kernel to the daemon.  It forced everybody to
link Unix sockets into the kernel but there are some people out there
who want to use it as a module.  Also the kernel code for communicating
with kerneld was "unpleasant", see ipc/msg.c in a 2.0 kernel.

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Re: [RFC] sane access to per-fs metadata (was Re: [PATCH]Documentation/ioctl-number.txt)

[Pjotr Kourzanoff]

On Fri, 23 Mar 2001, Bryan Henderson wrote:

> How it can be used? Well, say it you've mounted JFS on /usr/local
> >% mount -t jfsmeta none /mnt -o jfsroot=/usr/local
> >% ls /mnt
> >stats control   bootcode whatever_I_bloody_want
> >% cat /mnt/stats
> >master is on /usr/local
> >fragmentation = 5%
> >696942 reads, yodda, yodda
> >% echo "defrag 69 whatever 42 13" > /mnt/control
> >% umount /mnt
>
> There's a lot of cool simplicity in this, both in implementation and
> application, but it leaves something to be desired in functionality.  This
> is partly because the price you pay for being able to use existing,
> well-worn Unix interfaces is the ancient limitations of those interfaces
> -- like the inability to return adequate error information.

  I can imagine a solution to this using the _same_ method - extend
  /proc/*/ with a new entry (say, trace) for dumping errors. Put data
  in there from every failing function in your code. Normally, this
  will not introduce overheads (not unless you use error conditions to
  pass on useful information), however, in case of errors, you can
  get the backtrace (together with any info you want to put in there)
  immediately.

> Specifically, transactional stuff looks really hard in this method.
> If I want the user to know why his "defrag" command failed, how would I
> pass that information back to him?  What if I want to warn him of of a
> filesystem inconsistency I found along the way?  Or inform him of how
> effective the defrag was?  And bear in mind that multiple processes may be
> issuing commands to /mnt/control simultaneously.

  That's all up to you. Informational messages can go to /proc.
  Transactions/serialization can be done in your filesystem's
  implementation. Maybe glibc guys would even want to extend
  strerror() to handle these cases?

>
> With ioctl, I can easily match a response of any kind to a request.  I can
> even return an English text message if I want to be friendly.
>
> -
> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
> the body of a message to [EMAIL PROTECTED]
>

  Cheers,

Pjotr Kourzanov

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Re: [RFC] sane access to per-fs metadata (was Re: [PATCH] Documentation/ioctl-number.txt)

[Matthew Wilcox]

On Fri, Mar 23, 2001 at 09:56:47AM -0700, Bryan Henderson wrote:
> There's a lot of cool simplicity in this, both in implementation and 
> application, but it leaves something to be desired in functionality.  This 
> is partly because the price you pay for being able to use existing, 
> well-worn Unix interfaces is the ancient limitations of those interfaces 
> -- like the inability to return adequate error information.

hmm... open("defrag-error") first, then read from it if it fails?

> effective the defrag was?  And bear in mind that multiple processes may be 
> issuing commands to /mnt/control simultaneously.

you should probably serialise them.  you probably have to do this anyway.

> With ioctl, I can easily match a response of any kind to a request.  I can 
> even return an English text message if I want to be friendly.

yes, one of the nice plan9 changes was the change to returning strings
instead of numerics.

-- 
Revolutions do not require corporate support.
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Re: [RFC] sane access to per-fs metadata (was Re: [PATCH] Documentation/ioctl-number.txt)

[Bryan Henderson]

How it can be used? Well, say it you've mounted JFS on /usr/local
>% mount -t jfsmeta none /mnt -o jfsroot=/usr/local
>% ls /mnt
>stats control   bootcode whatever_I_bloody_want
>% cat /mnt/stats
>master is on /usr/local
>fragmentation = 5%
>696942 reads, yodda, yodda
>% echo "defrag 69 whatever 42 13" > /mnt/control
>% umount /mnt

There's a lot of cool simplicity in this, both in implementation and 
application, but it leaves something to be desired in functionality.  This 
is partly because the price you pay for being able to use existing, 
well-worn Unix interfaces is the ancient limitations of those interfaces 
-- like the inability to return adequate error information.

Specifically, transactional stuff looks really hard in this method.
If I want the user to know why his "defrag" command failed, how would I 
pass that information back to him?  What if I want to warn him of of a 
filesystem inconsistency I found along the way?  Or inform him of how 
effective the defrag was?  And bear in mind that multiple processes may be 
issuing commands to /mnt/control simultaneously.

With ioctl, I can easily match a response of any kind to a request.  I can 
even return an English text message if I want to be friendly.

-
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the body of a message to [EMAIL PROTECTED]
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Re: [RFC] sane access to per-fs metadata (was Re: [PATCH]Documentation/ioctl-number.txt)

[Dave Kleikamp]

Al,
I didn't know that creating file system ioctl's was such a hot topic. 
Since the functions I want to implement are for a very specific purpose
(I don't expect anything except the JFS utilities to invoke them), I
would expect an ioctl to be an appropriate vehicle.

If not ioctl's, why not procfs?  Your proposal is that each filesystem
implements its own mini-procfs.  What's the advantage of that?

My intentions so far are to use ioctl's for specific operations required
by the JFS utilities, and procfs for debugging output, tuning, and
anything else that make sense.

Alexander Viro wrote:
> That may look like an overkill, however
> * You can get rid of any need to register ioctls, etc.

This is a one-time thing

> * You can add debugging/whatever at any moment with no need to
>   update any utilities - everything is available from plain shell

We can do this with procfs right now.

> * You can conveniently view whatever metadata you want - no need to
>   shove everything into ioctls on one object.

Again, why re-invent procfs?  We could put this under
/proc/fs/jfs/metadata.

> * You can use normal permissions control - just set appropriate
>   permission bits for objects on jfsmeta
> 
> IOW, you can get normal filesystem view (meaning that you have all usual
> UNIX toolkit available) for per-fs control stuff. And keep the ability to
> do proper locking - it's the same driver that handles the main fs and you
> have access to superblock. No need to change the API - everything is already
> there...

I'm not sure how a utility would make atomic changes to several pieces
of metadata.  The underlying fs code would protect the integrity of
every metadata "file", but changes to more than one of these "files"
would not be done as a group without some additional locking that would
have to be coordinated between the utility and the fs.  This kind of
thing could be handled by writing some special command to a
"command-processor" type file, but why is this better than an ioctl?


-- 
David Kleikamp
IBM Linux Technology Center
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Re: [RFC] sane access to per-fs metadata (was Re: [PATCH] Documentation/ioctl-number.txt)

[Eric W. Biederman]

Alexander Viro <[EMAIL PROTECTED]> writes:

> IOW, you can get normal filesystem view (meaning that you have all usual
> UNIX toolkit available) for per-fs control stuff. And keep the ability to
> do proper locking - it's the same driver that handles the main fs and you
> have access to superblock. No need to change the API - everything is already
> there...
>   I'll post an example patch for ext2 (safe access to superblock,
> group descriptors, inode table and bitmaps on a live fs) after this weekend
> (== when misc shit will somewhat settle down).
>   Cheers,
>   Al
> 
> PS: Folks[1], I hope it explains why I'm very sceptical about "let's add new
> A{B,P}I" sort of ideas - approach above can be used for almost all stuff
> I've seen proposed. You can have multiple views of the same object. And
> have all of them available via normal API.


This is a cool idea.  But I couple of places where this might fall down.
1) If a filesystem has multiple name spaces and we use different mounts
   to handle them, will this break anything?  Fat32 with it's short and long
   names, and the Novell filesystem are the examples I can think of.

2) An API is still being developed it just uses the existing infrastructure
   which is good, but we still need to standardize what is exported.  It's
   a cleaner way to build a new API but a new API is being built.

3) What is a safe way to do this so a non-root user can call mount?

4) What is appropriate way using open,read,write,close,mount to handle stat data
   and extended attributes.  The stat data is the big one because it is used
   so frequently.  Possibly a mount/write syscall is needed.
   
   I keep thinking open("/path/to/file/stat_data") but that feels excessively heavy
   at the API level.   But if we involve mount (at least semantically)
   that could work for directories as well. 

The goal here is to push your ideas to the limits so we can where
using ioctl or new a syscall is appropriate.  If indeed there is such
a case.

Eric
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Re: [RFC] sane access to per-fs metadata (was Re: [PATCH]Documentation/ioctl-number.txt)

[Pjotr Kourzanoff]

On Fri, 23 Mar 2001, Bryan Henderson wrote:

 How it can be used? Well, say it you've mounted JFS on /usr/local
 % mount -t jfsmeta none /mnt -o jfsroot=/usr/local
 % ls /mnt
 stats control   bootcode whatever_I_bloody_want
 % cat /mnt/stats
 master is on /usr/local
 fragmentation = 5%
 696942 reads, yodda, yodda
 % echo "defrag 69 whatever 42 13"  /mnt/control
 % umount /mnt

 There's a lot of cool simplicity in this, both in implementation and
 application, but it leaves something to be desired in functionality.  This
 is partly because the price you pay for being able to use existing,
 well-worn Unix interfaces is the ancient limitations of those interfaces
 -- like the inability to return adequate error information.

  I can imagine a solution to this using the _same_ method - extend
  /proc/*/ with a new entry (say, trace) for dumping errors. Put data
  in there from every failing function in your code. Normally, this
  will not introduce overheads (not unless you use error conditions to
  pass on useful information), however, in case of errors, you can
  get the backtrace (together with any info you want to put in there)
  immediately.

 Specifically, transactional stuff looks really hard in this method.
 If I want the user to know why his "defrag" command failed, how would I
 pass that information back to him?  What if I want to warn him of of a
 filesystem inconsistency I found along the way?  Or inform him of how
 effective the defrag was?  And bear in mind that multiple processes may be
 issuing commands to /mnt/control simultaneously.

  That's all up to you. Informational messages can go to /proc.
  Transactions/serialization can be done in your filesystem's
  implementation. Maybe glibc guys would even want to extend
  strerror() to handle these cases?


 With ioctl, I can easily match a response of any kind to a request.  I can
 even return an English text message if I want to be friendly.

 -
 To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
 the body of a message to [EMAIL PROTECTED]


  Cheers,

Pjotr Kourzanov

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Re: [RFC] sane access to per-fs metadata (was Re: [PATCH] Documentation/ioctl-number.txt)

[Matthew Wilcox]

On Fri, Mar 23, 2001 at 09:56:47AM -0700, Bryan Henderson wrote:
 There's a lot of cool simplicity in this, both in implementation and 
 application, but it leaves something to be desired in functionality.  This 
 is partly because the price you pay for being able to use existing, 
 well-worn Unix interfaces is the ancient limitations of those interfaces 
 -- like the inability to return adequate error information.

hmm... open("defrag-error") first, then read from it if it fails?

 effective the defrag was?  And bear in mind that multiple processes may be 
 issuing commands to /mnt/control simultaneously.

you should probably serialise them.  you probably have to do this anyway.

 With ioctl, I can easily match a response of any kind to a request.  I can 
 even return an English text message if I want to be friendly.

yes, one of the nice plan9 changes was the change to returning strings
instead of numerics.

-- 
Revolutions do not require corporate support.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [EMAIL PROTECTED]
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Please read the FAQ at  http://www.tux.org/lkml/

Re: [RFC] sane access to per-fs metadata (was Re: [PATCH] Documentation/ioctl-number.txt)

[Bryan Henderson]

How it can be used? Well, say it you've mounted JFS on /usr/local
% mount -t jfsmeta none /mnt -o jfsroot=/usr/local
% ls /mnt
stats control   bootcode whatever_I_bloody_want
% cat /mnt/stats
master is on /usr/local
fragmentation = 5%
696942 reads, yodda, yodda
% echo "defrag 69 whatever 42 13"  /mnt/control
% umount /mnt

There's a lot of cool simplicity in this, both in implementation and 
application, but it leaves something to be desired in functionality.  This 
is partly because the price you pay for being able to use existing, 
well-worn Unix interfaces is the ancient limitations of those interfaces 
-- like the inability to return adequate error information.

Specifically, transactional stuff looks really hard in this method.
If I want the user to know why his "defrag" command failed, how would I 
pass that information back to him?  What if I want to warn him of of a 
filesystem inconsistency I found along the way?  Or inform him of how 
effective the defrag was?  And bear in mind that multiple processes may be 
issuing commands to /mnt/control simultaneously.

With ioctl, I can easily match a response of any kind to a request.  I can 
even return an English text message if I want to be friendly.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Re: [RFC] sane access to per-fs metadata (was Re: [PATCH]Documentation/ioctl-number.txt)

[Dave Kleikamp]

Al,
I didn't know that creating file system ioctl's was such a hot topic. 
Since the functions I want to implement are for a very specific purpose
(I don't expect anything except the JFS utilities to invoke them), I
would expect an ioctl to be an appropriate vehicle.

If not ioctl's, why not procfs?  Your proposal is that each filesystem
implements its own mini-procfs.  What's the advantage of that?

My intentions so far are to use ioctl's for specific operations required
by the JFS utilities, and procfs for debugging output, tuning, and
anything else that make sense.

Alexander Viro wrote:
 That may look like an overkill, however
 * You can get rid of any need to register ioctls, etc.

This is a one-time thing

 * You can add debugging/whatever at any moment with no need to
   update any utilities - everything is available from plain shell

We can do this with procfs right now.

 * You can conveniently view whatever metadata you want - no need to
   shove everything into ioctls on one object.

Again, why re-invent procfs?  We could put this under
/proc/fs/jfs/metadata.

 * You can use normal permissions control - just set appropriate
   permission bits for objects on jfsmeta
 
 IOW, you can get normal filesystem view (meaning that you have all usual
 UNIX toolkit available) for per-fs control stuff. And keep the ability to
 do proper locking - it's the same driver that handles the main fs and you
 have access to superblock. No need to change the API - everything is already
 there...

I'm not sure how a utility would make atomic changes to several pieces
of metadata.  The underlying fs code would protect the integrity of
every metadata "file", but changes to more than one of these "files"
would not be done as a group without some additional locking that would
have to be coordinated between the utility and the fs.  This kind of
thing could be handled by writing some special command to a
"command-processor" type file, but why is this better than an ioctl?


-- 
David Kleikamp
IBM Linux Technology Center
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Re: [RFC] sane access to per-fs metadata (was Re: [PATCH] Documentation/ioctl-number.txt)

[Eric W. Biederman]

Alexander Viro [EMAIL PROTECTED] writes:

 IOW, you can get normal filesystem view (meaning that you have all usual
 UNIX toolkit available) for per-fs control stuff. And keep the ability to
 do proper locking - it's the same driver that handles the main fs and you
 have access to superblock. No need to change the API - everything is already
 there...
   I'll post an example patch for ext2 (safe access to superblock,
 group descriptors, inode table and bitmaps on a live fs) after this weekend
 (== when misc shit will somewhat settle down).
   Cheers,
   Al
 
 PS: Folks[1], I hope it explains why I'm very sceptical about "let's add new
 A{B,P}I" sort of ideas - approach above can be used for almost all stuff
 I've seen proposed. You can have multiple views of the same object. And
 have all of them available via normal API.


This is a cool idea.  But I couple of places where this might fall down.
1) If a filesystem has multiple name spaces and we use different mounts
   to handle them, will this break anything?  Fat32 with it's short and long
   names, and the Novell filesystem are the examples I can think of.

2) An API is still being developed it just uses the existing infrastructure
   which is good, but we still need to standardize what is exported.  It's
   a cleaner way to build a new API but a new API is being built.

3) What is a safe way to do this so a non-root user can call mount?

4) What is appropriate way using open,read,write,close,mount to handle stat data
   and extended attributes.  The stat data is the big one because it is used
   so frequently.  Possibly a mountopenread/writecloseumount syscall is needed.
   
   I keep thinking open("/path/to/file/stat_data") but that feels excessively heavy
   at the API level.   But if we involve mount (at least semantically)
   that could work for directories as well. 

The goal here is to push your ideas to the limits so we can where
using ioctl or new a syscall is appropriate.  If indeed there is such
a case.

Eric
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