vfs: Allow handle based open on symlinks
in [Kernel]
|
From: Nick Piggin on 7 Jul 2010 11:30 On Tue, Jun 15, 2010 at 10:42:54PM +0530, Aneesh Kumar K.V wrote: > The patch update may_open to allow handle based open on symlinks. > The file handle based API use file descritor returned from open_by_handle_at > to do different file system operations. To find the link target name we > need to get a file descriptor on symlinks. This is a pretty big change, isn't it? Have you looked through vfs to ensure this is actually OK? I was just looking at remount,ro code, for example, and it seems to assume only writable open files on ISREG files. Is this restricted to RDONLY? Really, it should be O_NONE... -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Aneesh Kumar K. V on 7 Jul 2010 12:30 On Thu, 8 Jul 2010 01:23:03 +1000, Nick Piggin <npiggin(a)suse.de> wrote: > On Tue, Jun 15, 2010 at 10:42:54PM +0530, Aneesh Kumar K.V wrote: > > The patch update may_open to allow handle based open on symlinks. > > The file handle based API use file descritor returned from open_by_handle_at > > to do different file system operations. To find the link target name we > > need to get a file descriptor on symlinks. > > This is a pretty big change, isn't it? Yes > Have you looked through vfs to > ensure this is actually OK? I was just looking at remount,ro code, for > example, and it seems to assume only writable open files on ISREG > files. I verified that write and read returns an error on that descriptor. I will look at rest of code to ensure the it doesn't break assumptions in the rest of VFS. > > Is this restricted to RDONLY? Really, it should be O_NONE... > > we need the interface so that we can do fstat(lstat) and readlink using the handle. If we are against the idea of allowing an fd on symlink, how about adding stat_by_handle and readlink_by_handle syscall ? That way we can drop "vfs: Support null pathname in readlink" patch -aneesh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Nick Piggin on 7 Jul 2010 12:50 On Tue, Jun 15, 2010 at 10:42:54PM +0530, Aneesh Kumar K.V wrote: > The patch update may_open to allow handle based open on symlinks. > The file handle based API use file descritor returned from open_by_handle_at > to do different file system operations. To find the link target name we > need to get a file descriptor on symlinks. > > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar(a)linux.vnet.ibm.com> > --- > fs/namei.c | 17 ++++++++++++++--- > 1 files changed, 14 insertions(+), 3 deletions(-) > > diff --git a/fs/namei.c b/fs/namei.c > index c2d19c7..417bf53 100644 > --- a/fs/namei.c > +++ b/fs/namei.c > @@ -1422,7 +1422,7 @@ int vfs_create(struct inode *dir, struct dentry *dentry, int mode, > return error; > } > > -int may_open(struct path *path, int acc_mode, int flag) > +static int __may_open(struct path *path, int acc_mode, int flag, int handle) > { > struct dentry *dentry = path->dentry; > struct inode *inode = dentry->d_inode; > @@ -1433,7 +1433,13 @@ int may_open(struct path *path, int acc_mode, int flag) > > switch (inode->i_mode & S_IFMT) { > case S_IFLNK: > - return -ELOOP; > + /* > + * For file handle based open we should allow > + * open of symlink. > + */ > + if (!handle) > + return -ELOOP; > + break; > case S_IFDIR: > if (acc_mode & MAY_WRITE) > return -EISDIR; > @@ -1473,6 +1479,11 @@ int may_open(struct path *path, int acc_mode, int flag) > return break_lease(inode, flag); > } > > +int may_open(struct path *path, int acc_mode, int flag) > +{ > + return __may_open(path, acc_mode, flag, 0); > +} Why don't you just add MAY_OPEN_LNK instead of this ugliness? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Nick Piggin on 7 Jul 2010 13:00 On Wed, Jul 07, 2010 at 09:54:52PM +0530, Aneesh Kumar K. V wrote: > On Thu, 8 Jul 2010 01:23:03 +1000, Nick Piggin <npiggin(a)suse.de> wrote: > > On Tue, Jun 15, 2010 at 10:42:54PM +0530, Aneesh Kumar K.V wrote: > > > The patch update may_open to allow handle based open on symlinks. > > > The file handle based API use file descritor returned from open_by_handle_at > > > to do different file system operations. To find the link target name we > > > need to get a file descriptor on symlinks. > > > > This is a pretty big change, isn't it? > > Yes > > > Have you looked through vfs to > > ensure this is actually OK? I was just looking at remount,ro code, for > > example, and it seems to assume only writable open files on ISREG > > files. > > I verified that write and read returns an error on that descriptor. I > will look at rest of code to ensure the it doesn't break assumptions in > the rest of VFS. > > > > > Is this restricted to RDONLY? Really, it should be O_NONE... > > > > > > we need the interface so that we can do fstat(lstat) and readlink using the > handle. If we are against the idea of allowing an fd on symlink, how about > adding stat_by_handle and readlink_by_handle syscall ? That way we can > drop "vfs: Support null pathname in readlink" patch It would be nice to avoid introducing open files to symlinks, but I don't know about really the *right* thing to do though. I think avoiding adding any by-handle syscalls except for open by handle may be a good idea... OTOH if this is really a special case for handles... I haven't followed this thread closely, so can you just go back and explain to me why you need this? Ie. that you can't achieve with a path-to-handle follow/nofollow option. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Aneesh Kumar K. V on 7 Jul 2010 14:00
On Thu, 8 Jul 2010 02:57:19 +1000, Nick Piggin <npiggin(a)suse.de> wrote: > On Wed, Jul 07, 2010 at 09:54:52PM +0530, Aneesh Kumar K. V wrote: > > On Thu, 8 Jul 2010 01:23:03 +1000, Nick Piggin <npiggin(a)suse.de> wrote: > > > On Tue, Jun 15, 2010 at 10:42:54PM +0530, Aneesh Kumar K.V wrote: > > > > The patch update may_open to allow handle based open on symlinks. > > > > The file handle based API use file descritor returned from open_by_handle_at > > > > to do different file system operations. To find the link target name we > > > > need to get a file descriptor on symlinks. > > > > > > This is a pretty big change, isn't it? > > > > Yes > > > > > Have you looked through vfs to > > > ensure this is actually OK? I was just looking at remount,ro code, for > > > example, and it seems to assume only writable open files on ISREG > > > files. > > > > I verified that write and read returns an error on that descriptor. I > > will look at rest of code to ensure the it doesn't break assumptions in > > the rest of VFS. > > > > > > > > Is this restricted to RDONLY? Really, it should be O_NONE... > > > > > > > > > > we need the interface so that we can do fstat(lstat) and readlink using the > > handle. If we are against the idea of allowing an fd on symlink, how about > > adding stat_by_handle and readlink_by_handle syscall ? That way we can > > drop "vfs: Support null pathname in readlink" patch > > It would be nice to avoid introducing open files to symlinks, but > I don't know about really the *right* thing to do though. I think > avoiding adding any by-handle syscalls except for open by handle > may be a good idea... OTOH if this is really a special case for > handles... > > I haven't followed this thread closely, so can you just go back > and explain to me why you need this? Ie. that you can't achieve with > a path-to-handle follow/nofollow option. We need to be able to read the link target using file handle. The exact usecase i have is with respect to implementing READLINK operation on a userspace NFS server. The request contain the file handle and the response include target name. Similarly we need to able to get file attribute based on file handle. I was using readlinkat and fstat to obtain both the above information using the descriptor returned by open_by_handle on a file handle representing symlink -aneesh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |