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Date: Thu, 13 May 2010 09:44:22 +1000
From: Neil Brown <neilb@...e.de>
To: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc: hch@...radead.org, viro@...iv.linux.org.uk, adilger@....com,
corbet@....net, serue@...ibm.com, linux-fsdevel@...r.kernel.org,
sfrench@...ibm.com, philippe.deniel@....FR,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH -V7 4/9] vfs: Add open by file handle support
On Wed, 12 May 2010 21:20:39 +0530
"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> wrote:
> Acked-by: Serge Hallyn <serue@...ibm.com>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> ---
> fs/namei.c | 24 ---------
> fs/open.c | 136 +++++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/namei.h | 24 +++++++++
> 3 files changed, 160 insertions(+), 24 deletions(-)
>
> diff --git a/fs/namei.c b/fs/namei.c
> index a7dce91..a18711e 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -1521,30 +1521,6 @@ out_unlock:
> return may_open(&nd->path, 0, open_flag & ~O_TRUNC);
> }
>
> -/*
> - * Note that while the flag value (low two bits) for sys_open means:
> - * 00 - read-only
> - * 01 - write-only
> - * 10 - read-write
> - * 11 - special
> - * it is changed into
> - * 00 - no permissions needed
> - * 01 - read-permission
> - * 10 - write-permission
> - * 11 - read-write
> - * for the internal routines (ie open_namei()/follow_link() etc)
> - * This is more logical, and also allows the 00 "no perm needed"
> - * to be used for symlinks (where the permissions are checked
> - * later).
> - *
> -*/
> -static inline int open_to_namei_flags(int flag)
> -{
> - if ((flag+1) & O_ACCMODE)
> - flag++;
> - return flag;
> -}
> -
> static int open_will_truncate(int flag, struct inode *inode)
> {
> /*
> diff --git a/fs/open.c b/fs/open.c
> index 9a34b81..348a1b9 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -1315,3 +1315,139 @@ err_out:
> asmlinkage_protect(4, ret, dfd, name, handle, flag);
> return ret;
> }
> +
> +static int vfs_dentry_acceptable(void *context, struct dentry *dentry)
> +{
> + return 1;
> +}
> +
> +static struct dentry *handle_to_dentry(struct vfsmount *mnt,
> + struct file_handle *handle)
> +{
> + int handle_size;
> + struct dentry *dentry;
> +
> + /* change the handle size to multiple of sizeof(u32) */
> + handle_size = handle->handle_size >> 2;
> + dentry = exportfs_decode_fh(mnt, (struct fid *)handle->f_handle,
> + handle_size, handle->handle_type,
> + vfs_dentry_acceptable, NULL);
> + return dentry;
> +}
> +
> +static long do_sys_open_by_handle(struct file_handle __user *ufh, int flags)
> +{
> + int fd;
> + int retval = 0;
> + int d_flags = flags;
> + struct file *filp;
> + struct vfsmount *mnt;
> + struct inode *inode;
> + struct dentry *dentry;
> + struct file_handle f_handle;
> + struct file_handle *handle = NULL;
> +
> + if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) {
> + retval = -EFAULT;
> + goto out_err;
> + }
> + if ((f_handle.handle_size > MAX_HANDLE_SZ) ||
> + (f_handle.handle_size <= 0)) {
> + retval = -EINVAL;
> + goto out_err;
> + }
> + if (!capable(CAP_DAC_OVERRIDE)) {
> + retval = -EPERM;
> + goto out_err;
> + }
> + /*
> + * Find the vfsmount for this uuid in the
> + * current namespace
> + */
> + mnt = fs_get_vfsmount(current, &f_handle.fsid);
> + if (!mnt) {
> + retval = -ESTALE;
> + goto out_err;
> + }
> +
> + handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_size,
> + GFP_KERNEL);
> + if (!handle) {
> + retval = -ENOMEM;
> + goto out_mnt;
> + }
> + /* copy the full handle */
> + if (copy_from_user(handle, ufh,
> + sizeof(struct file_handle) +
> + f_handle.handle_size)) {
> + retval = -EFAULT;
> + goto out_mnt;
> + }
> + dentry = handle_to_dentry(mnt, handle);
> + if (IS_ERR(dentry)) {
> + retval = PTR_ERR(dentry);
> + goto out_mnt;
> + }
> + inode = dentry->d_inode;
> + flags = open_to_namei_flags(flags);
> + /* O_TRUNC implies we need access checks for write permissions */
> + if (flags & O_TRUNC)
> + flags |= MAY_WRITE;
> +
> + if ((!(flags & O_APPEND) || (flags & O_TRUNC)) &&
> + (flags & FMODE_WRITE) && IS_APPEND(inode)) {
> + retval = -EPERM;
> + goto out_dentry;
> + }
> + if ((flags & FMODE_WRITE) && IS_IMMUTABLE(inode)) {
> + retval = -EACCES;
> + goto out_dentry;
> + }
> + /* Can't write directories. */
> + if (S_ISDIR(inode->i_mode) && (flags & FMODE_WRITE)) {
> + retval = -EISDIR;
> + goto out_dentry;
> + }
Including all these checks inline here seems error prone. Can you not just
use finish_open ?? It might do more than you need, but it would be more
obvious that you didn't forget anything..
> + fd = get_unused_fd_flags(d_flags);
> + if (fd < 0) {
> + retval = fd;
> + goto out_dentry;
> + }
> + filp = dentry_open(dget(dentry), mntget(mnt),
> + d_flags, current_cred());
> + if (IS_ERR(filp)) {
> + put_unused_fd(fd);
> + retval = PTR_ERR(filp);
> + goto out_dentry;
> + }
> + if (inode->i_mode & S_IFREG) {
I suspect this is not the test you want. It tests for IFREG or IFLNK or
IFSOCK.
> + filp->f_flags |= O_NOATIME;
> + filp->f_mode |= FMODE_NOCMTIME;
> + }
I think you need a comment here explaining the rational for these setting.
Why is O_NOATIME important IFREG but not for IFDIR?
Why is it not sufficient to honour O_NOATIME that is passed in.
How can you ever justify setting FMODE_NOCMTIME ?
I guess you are just copying from xfs code, but it still needs justification.
NeilBrown
> + fsnotify_open(filp->f_path.dentry);
> + fd_install(fd, filp);
> + retval = fd;
> +
> +out_dentry:
> + dput(dentry);
> +out_mnt:
> + kfree(handle);
> + mntput(mnt);
> +out_err:
> + return retval;
> +}
> +
> +SYSCALL_DEFINE2(open_by_handle, struct file_handle __user *, handle,
> + int, flags)
> +{
> + long ret;
> +
> + if (force_o_largefile())
> + flags |= O_LARGEFILE;
> +
> + ret = do_sys_open_by_handle(handle, flags);
> +
> + /* avoid REGPARM breakage on x86: */
> + asmlinkage_protect(2, ret, handle, flags);
> + return ret;
> +}
> diff --git a/include/linux/namei.h b/include/linux/namei.h
> index 05b441d..a853aa0 100644
> --- a/include/linux/namei.h
> +++ b/include/linux/namei.h
> @@ -4,6 +4,7 @@
> #include <linux/dcache.h>
> #include <linux/linkage.h>
> #include <linux/path.h>
> +#include <asm-generic/fcntl.h>
>
> struct vfsmount;
>
> @@ -96,4 +97,27 @@ static inline void nd_terminate_link(void *name, size_t len, size_t maxlen)
> ((char *) name)[min(len, maxlen)] = '\0';
> }
>
> +/*
> + * Note that while the flag value (low two bits) for sys_open means:
> + * 00 - read-only
> + * 01 - write-only
> + * 10 - read-write
> + * 11 - special
> + * it is changed into
> + * 00 - no permissions needed
> + * 01 - read-permission
> + * 10 - write-permission
> + * 11 - read-write
> + * for the internal routines (ie open_namei()/follow_link() etc)
> + * This is more logical, and also allows the 00 "no perm needed"
> + * to be used for symlinks (where the permissions are checked
> + * later).
> + *
> +*/
> +static inline int open_to_namei_flags(int flag)
> +{
> + if ((flag+1) & O_ACCMODE)
> + flag++;
> + return flag;
> +}
> #endif /* _LINUX_NAMEI_H */
--
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