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    SubjectRe: [PATCH -V14 04/11] vfs: Allow handle based open on symlinks
    Date
    On Thu, 8 Jul 2010 02:48:59 +1000, Nick Piggin <npiggin@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.
    > >
    > > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@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?
    >

    Something like the below ?

    commit 69787f5ed6c8a7a63ad21ef5d7de0b62f124ff0a
    Author: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    Date: Tue Jul 6 23:25:57 2010 +0530

    vfs: Allow handle based open on symlinks

    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@linux.vnet.ibm.com>

    diff --git a/fs/namei.c b/fs/namei.c
    index de40312..2ea5c79 100644
    --- a/fs/namei.c
    +++ b/fs/namei.c
    @@ -1456,7 +1456,15 @@ int may_open(struct path *path, int acc_mode, int flag)

    switch (inode->i_mode & S_IFMT) {
    case S_IFLNK:
    - return -ELOOP;
    + /*
    + * Allow only if acc_mode contain
    + * open link request and read request.
    + */
    + if (acc_mode != (MAY_OPEN_LINK | MAY_READ))
    + return -ELOOP;
    + if (flag != O_RDONLY)
    + return -ELOOP;
    + break;
    case S_IFDIR:
    if (acc_mode & MAY_WRITE)
    return -EISDIR;
    diff --git a/fs/open.c b/fs/open.c
    index daf2534..a58837a 100644
    --- a/fs/open.c
    +++ b/fs/open.c
    @@ -1266,8 +1266,15 @@ static long do_sys_open_by_handle(int mountdirfd,
    */
    if (open_flag & __O_SYNC)
    open_flag |= O_DSYNC;
    + /*
    + * Handle based API allow open on a symlink
    + */
    + if (S_ISLNK(path->dentry->d_inode->i_mode))
    + acc_mode = MAY_OPEN_LINK;
    + else
    + acc_mode = MAY_OPEN;

    - acc_mode = MAY_OPEN | ACC_MODE(open_flag);
    + acc_mode |= ACC_MODE(open_flag);

    /* O_TRUNC implies we need access checks for write permissions */
    if (open_flag & O_TRUNC)
    diff --git a/include/linux/fs.h b/include/linux/fs.h
    index cbff4ca..eaf13d1 100644
    --- a/include/linux/fs.h
    +++ b/include/linux/fs.h
    @@ -53,6 +53,7 @@ struct inodes_stat_t {
    #define MAY_APPEND 8
    #define MAY_ACCESS 16
    #define MAY_OPEN 32
    +#define MAY_OPEN_LINK 64

    /*
    * flags in file.f_mode. Note that FMODE_READ and FMODE_WRITE must correspond

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