* [PATCH] Make file struct available to fchmod FS handlers.
@ 2016-11-02 22:53 Jose Lopes
2016-11-03 0:59 ` Al Viro
2016-11-07 5:25 ` Nikolaus Rath
0 siblings, 2 replies; 12+ messages in thread
From: Jose Lopes @ 2016-11-02 22:53 UTC (permalink / raw)
To: Alexander Viro; +Cc: Jose Lopes, linux-fsdevel, fuse-devel
Syscall 'ftruncate' makes the 'file' struct available to filesystem
handlers. This makes it possible, e.g., for filesystems, such as,
FUSE, to access the file handle associated with the file descriptor
that was passed to 'ftruncate'. In the specific case of FUSE, this
also makes it possible for (userspace) FUSE-based filesystems to
distinguish between calls to 'truncate' and 'ftruncate'.
>From an implementation point of view, this is possible because the
'ftruncate' syscall passes the 'file' struct to the underlying
filesystem handlers via the 'ia_file' field and the 'ia_valid' field
mask.
Similarly to 'ftruncate', pass the 'file' struct to 'fchmod', which
allows filesystem handlers to get the file handle associated with the
file descriptor passed to 'fchmod' and allows FUSE-based filesystems
to distinguish between calls to 'chmod' and 'fchmod'.
In a future patch, make a similar change to the 'fchown' and
'futimens' syscalls.
Signed-off-by: Jose Lopes <jabolopes@gmail.com>
---
fs/open.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/fs/open.c b/fs/open.c
index d3ed817..00214c5 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -516,7 +516,8 @@ SYSCALL_DEFINE1(chroot, const char __user *, filename)
return error;
}
-static int chmod_common(const struct path *path, umode_t mode)
+static int chmod_common(const struct path *path, umode_t mode,
+ struct file *filp)
{
struct inode *inode = path->dentry->d_inode;
struct inode *delegated_inode = NULL;
@@ -533,6 +534,10 @@ static int chmod_common(const struct path *path, umode_t mode)
goto out_unlock;
newattrs.ia_mode = (mode & S_IALLUGO) | (inode->i_mode & ~S_IALLUGO);
newattrs.ia_valid = ATTR_MODE | ATTR_CTIME;
+ if (filp) {
+ newattrs.ia_file = filp;
+ newattrs.ia_valid |= ATTR_FILE;
+ }
error = notify_change(path->dentry, &newattrs, &delegated_inode);
out_unlock:
inode_unlock(inode);
@@ -552,7 +557,7 @@ SYSCALL_DEFINE2(fchmod, unsigned int, fd, umode_t, mode)
if (f.file) {
audit_file(f.file);
- err = chmod_common(&f.file->f_path, mode);
+ err = chmod_common(&f.file->f_path, mode, f.file);
fdput(f);
}
return err;
@@ -566,7 +571,7 @@ SYSCALL_DEFINE3(fchmodat, int, dfd, const char __user *, filename, umode_t, mode
retry:
error = user_path_at(dfd, filename, lookup_flags, &path);
if (!error) {
- error = chmod_common(&path, mode);
+ error = chmod_common(&path, mode, NULL);
path_put(&path);
if (retry_estale(error, lookup_flags)) {
lookup_flags |= LOOKUP_REVAL;
--
2.9.0
^ permalink raw reply related [flat|nested] 12+ messages in thread
* Re: [PATCH] Make file struct available to fchmod FS handlers.
2016-11-02 22:53 [PATCH] Make file struct available to fchmod FS handlers Jose Lopes
@ 2016-11-03 0:59 ` Al Viro
2016-11-03 8:22 ` [fuse-devel] " Jean-Pierre André
2016-11-03 15:22 ` Nikolaus Rath
2016-11-07 5:25 ` Nikolaus Rath
1 sibling, 2 replies; 12+ messages in thread
From: Al Viro @ 2016-11-03 0:59 UTC (permalink / raw)
To: Jose Lopes; +Cc: linux-fsdevel, fuse-devel
On Wed, Nov 02, 2016 at 11:53:40PM +0100, Jose Lopes wrote:
> Syscall 'ftruncate' makes the 'file' struct available to filesystem
> handlers. This makes it possible, e.g., for filesystems, such as,
> FUSE, to access the file handle associated with the file descriptor
> that was passed to 'ftruncate'. In the specific case of FUSE, this
> also makes it possible for (userspace) FUSE-based filesystems to
> distinguish between calls to 'truncate' and 'ftruncate'.
Why FUSE is such a precious snowflake that it needs to make that distinction,
unlike all other filesystems?
> In a future patch, make a similar change to the 'fchown' and
> 'futimens' syscalls.
I'm thucking frilled...
NAK, unless you can give a better reason than "what if somebody would want
that piece of information?".
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [fuse-devel] [PATCH] Make file struct available to fchmod FS handlers.
2016-11-03 0:59 ` Al Viro
@ 2016-11-03 8:22 ` Jean-Pierre André
[not found] ` <581AF3CB.3090001-39ZsbGIQGT5GWvitb5QawA@public.gmane.org>
2016-11-03 15:22 ` Nikolaus Rath
1 sibling, 1 reply; 12+ messages in thread
From: Jean-Pierre André @ 2016-11-03 8:22 UTC (permalink / raw)
To: Al Viro, Jose Lopes; +Cc: linux-fsdevel, fuse-devel
Al Viro wrote:
> On Wed, Nov 02, 2016 at 11:53:40PM +0100, Jose Lopes wrote:
>> Syscall 'ftruncate' makes the 'file' struct available to filesystem
>> handlers. This makes it possible, e.g., for filesystems, such as,
>> FUSE, to access the file handle associated with the file descriptor
>> that was passed to 'ftruncate'. In the specific case of FUSE, this
>> also makes it possible for (userspace) FUSE-based filesystems to
>> distinguish between calls to 'truncate' and 'ftruncate'.
>
> Why FUSE is such a precious snowflake that it needs to make that distinction,
> unlike all other filesystems?
For fuse file system which delegate the permission checks
to user space (and have to do so because of cacheing
issues), the write permission has to be checked for
truncate(), and not checked for ftruncate() : the file
may have been opened for writing and then its permissions
set to read-only before the ftruncate() is requested.
The user space file system can check current permissions,
not the ones which were set when the file was opened.
Jean-Pierre
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] Make file struct available to fchmod FS handlers.
2016-11-03 0:59 ` Al Viro
2016-11-03 8:22 ` [fuse-devel] " Jean-Pierre André
@ 2016-11-03 15:22 ` Nikolaus Rath
2016-11-07 4:51 ` Nikolaus Rath
1 sibling, 1 reply; 12+ messages in thread
From: Nikolaus Rath @ 2016-11-03 15:22 UTC (permalink / raw)
To: Al Viro; +Cc: Jose Lopes, linux-fsdevel, fuse-devel
On Nov 03 2016, Al Viro <viro@ZenIV.linux.org.uk> wrote:
> On Wed, Nov 02, 2016 at 11:53:40PM +0100, Jose Lopes wrote:
>> Syscall 'ftruncate' makes the 'file' struct available to filesystem
>> handlers. This makes it possible, e.g., for filesystems, such as,
>> FUSE, to access the file handle associated with the file descriptor
>> that was passed to 'ftruncate'. In the specific case of FUSE, this
>> also makes it possible for (userspace) FUSE-based filesystems to
>> distinguish between calls to 'truncate' and 'ftruncate'.
>
> Why FUSE is such a precious snowflake that it needs to make that distinction,
> unlike all other filesystems?
FUSE filesystems are often used as an extra layer on top of another
filesystem (that stores the actual data). If the user opens a file (in
the fuse filesystem), deletes it, and then truncates it, FUSE currently
cannot do the same operation in the underlying filesystem: it receives
a truncate() call with the inode, but there is no syscall that allows
truncation for an inode. If FUSE had access to the file handle, it can
use that to store a file descriptor for the file on the underlying
filesystem and use ftruncate.
Best,
-Nikolaus
--
GPG encrypted emails preferred. Key id: 0xD113FCAC3C4E599F
Fingerprint: ED31 791B 2C5C 1613 AF38 8B8A D113 FCAC 3C4E 599F
»Time flies like an arrow, fruit flies like a Banana.«
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] Make file struct available to fchmod FS handlers.
2016-11-03 15:22 ` Nikolaus Rath
@ 2016-11-07 4:51 ` Nikolaus Rath
2016-11-09 17:54 ` Jose Lopes
0 siblings, 1 reply; 12+ messages in thread
From: Nikolaus Rath @ 2016-11-07 4:51 UTC (permalink / raw)
To: Al Viro; +Cc: Jose Lopes, linux-fsdevel, fuse-devel
On Nov 03 2016, Nikolaus Rath <Nikolaus-BTH8mxji4b0@public.gmane.org> wrote:
> On Nov 03 2016, Al Viro <viro@ZenIV.linux.org.uk> wrote:
>> On Wed, Nov 02, 2016 at 11:53:40PM +0100, Jose Lopes wrote:
>>> Syscall 'ftruncate' makes the 'file' struct available to filesystem
>>> handlers. This makes it possible, e.g., for filesystems, such as,
>>> FUSE, to access the file handle associated with the file descriptor
>>> that was passed to 'ftruncate'. In the specific case of FUSE, this
>>> also makes it possible for (userspace) FUSE-based filesystems to
>>> distinguish between calls to 'truncate' and 'ftruncate'.
>>
>> Why FUSE is such a precious snowflake that it needs to make that distinction,
>> unlike all other filesystems?
>
> FUSE filesystems are often used as an extra layer on top of another
> filesystem (that stores the actual data). If the user opens a file (in
> the fuse filesystem), deletes it, and then truncates it, FUSE currently
> cannot do the same operation in the underlying filesystem: it receives
> a truncate() call with the inode, but there is no syscall that allows
> truncation for an inode. If FUSE had access to the file handle, it can
> use that to store a file descriptor for the file on the underlying
> filesystem and use ftruncate.
In case it wasn't clear: for the case of ftruncate, fuse *does* have
access to the file handle so the problem does not arise. For the case of
fchmod, this is currently a problem (and the patch we're discussing
would fix it).
Best,
-Nikolaus
--
GPG encrypted emails preferred. Key id: 0xD113FCAC3C4E599F
Fingerprint: ED31 791B 2C5C 1613 AF38 8B8A D113 FCAC 3C4E 599F
»Time flies like an arrow, fruit flies like a Banana.«
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] Make file struct available to fchmod FS handlers.
2016-11-07 4:51 ` Nikolaus Rath
@ 2016-11-09 17:54 ` Jose Lopes
0 siblings, 0 replies; 12+ messages in thread
From: Jose Lopes @ 2016-11-09 17:54 UTC (permalink / raw)
To: Al Viro; +Cc: linux-fsdevel, fuse-devel, Jean-Pierre André, Nikolaus
Hi Al,
Can you please take another look?
Thanks,
Jose
On Mon, Nov 7, 2016 at 5:51 AM, Nikolaus Rath <Nikolaus@rath.org> wrote:
> On Nov 03 2016, Nikolaus Rath <Nikolaus-BTH8mxji4b0@public.gmane.org> wrote:
>> On Nov 03 2016, Al Viro <viro@ZenIV.linux.org.uk> wrote:
>>> On Wed, Nov 02, 2016 at 11:53:40PM +0100, Jose Lopes wrote:
>>>> Syscall 'ftruncate' makes the 'file' struct available to filesystem
>>>> handlers. This makes it possible, e.g., for filesystems, such as,
>>>> FUSE, to access the file handle associated with the file descriptor
>>>> that was passed to 'ftruncate'. In the specific case of FUSE, this
>>>> also makes it possible for (userspace) FUSE-based filesystems to
>>>> distinguish between calls to 'truncate' and 'ftruncate'.
>>>
>>> Why FUSE is such a precious snowflake that it needs to make that distinction,
>>> unlike all other filesystems?
>>
>> FUSE filesystems are often used as an extra layer on top of another
>> filesystem (that stores the actual data). If the user opens a file (in
>> the fuse filesystem), deletes it, and then truncates it, FUSE currently
>> cannot do the same operation in the underlying filesystem: it receives
>> a truncate() call with the inode, but there is no syscall that allows
>> truncation for an inode. If FUSE had access to the file handle, it can
>> use that to store a file descriptor for the file on the underlying
>> filesystem and use ftruncate.
>
> In case it wasn't clear: for the case of ftruncate, fuse *does* have
> access to the file handle so the problem does not arise. For the case of
> fchmod, this is currently a problem (and the patch we're discussing
> would fix it).
>
> Best,
> -Nikolaus
>
> --
> GPG encrypted emails preferred. Key id: 0xD113FCAC3C4E599F
> Fingerprint: ED31 791B 2C5C 1613 AF38 8B8A D113 FCAC 3C4E 599F
>
> »Time flies like an arrow, fruit flies like a Banana.«
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] Make file struct available to fchmod FS handlers.
2016-11-02 22:53 [PATCH] Make file struct available to fchmod FS handlers Jose Lopes
2016-11-03 0:59 ` Al Viro
@ 2016-11-07 5:25 ` Nikolaus Rath
1 sibling, 0 replies; 12+ messages in thread
From: Nikolaus Rath @ 2016-11-07 5:25 UTC (permalink / raw)
To: Jose Lopes; +Cc: Alexander Viro, linux-fsdevel, fuse-devel
On Nov 03 2016, Jose Lopes <jabolopes@gmail.com> wrote:
> Syscall 'ftruncate' makes the 'file' struct available to filesystem
> handlers. This makes it possible, e.g., for filesystems, such as,
> FUSE, to access the file handle associated with the file descriptor
> that was passed to 'ftruncate'. In the specific case of FUSE, this
> also makes it possible for (userspace) FUSE-based filesystems to
> distinguish between calls to 'truncate' and 'ftruncate'.
>
> From an implementation point of view, this is possible because the
> 'ftruncate' syscall passes the 'file' struct to the underlying
> filesystem handlers via the 'ia_file' field and the 'ia_valid' field
> mask.
>
> Similarly to 'ftruncate', pass the 'file' struct to 'fchmod', which
> allows filesystem handlers to get the file handle associated with the
> file descriptor passed to 'fchmod' and allows FUSE-based filesystems
> to distinguish between calls to 'chmod' and 'fchmod'.
>
> In a future patch, make a similar change to the 'fchown' and
> 'futimens' syscalls.
>
> Signed-off-by: Jose Lopes <jabolopes@gmail.com>
Tested-by: Nikolaus Rath <Nikolaus@rath.org>
Best,
-Nikolaus
--
GPG encrypted emails preferred. Key id: 0xD113FCAC3C4E599F
Fingerprint: ED31 791B 2C5C 1613 AF38 8B8A D113 FCAC 3C4E 599F
»Time flies like an arrow, fruit flies like a Banana.«
^ permalink raw reply [flat|nested] 12+ messages in thread
end of thread, other threads:[~2016-11-17 23:03 UTC | newest]
Thread overview: 12+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-11-02 22:53 [PATCH] Make file struct available to fchmod FS handlers Jose Lopes
2016-11-03 0:59 ` Al Viro
2016-11-03 8:22 ` [fuse-devel] " Jean-Pierre André
[not found] ` <581AF3CB.3090001-39ZsbGIQGT5GWvitb5QawA@public.gmane.org>
2016-11-03 10:26 ` Jose Lopes
2016-11-17 17:44 ` [fuse-devel] " Eric W. Biederman
2016-11-17 18:39 ` Nikolaus Rath
2016-11-17 19:20 ` Eric W. Biederman
2016-11-17 23:03 ` Stef Bon
2016-11-03 15:22 ` Nikolaus Rath
2016-11-07 4:51 ` Nikolaus Rath
2016-11-09 17:54 ` Jose Lopes
2016-11-07 5:25 ` Nikolaus Rath
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