On 2011-11-05 08:30:02, Tyler Hicks wrote:
> On 2011-10-31 12:14:05, Thieu Le wrote:
> > Export fallocate facility so layered file systems such as ecryptfs can
> > take advantage of this feature. One example of the need for fallocate
> > is by ecryptfs. ecryptfs has recently switched to a writeback cache
> > model so its dirty pages are not written to the lower file system
> > immediately. In order to ensure that space is available when the page
> > is later written, ecryptfs can efficiently preallocate that space using
> > vfs_fallocate().
>
> Hi Thieu - Thanks for the patch. Something like this is definitely
> needed for eCryptfs.
>
> >
> > vfs_fallocate() does not perform all of the checkings of do_fallocate()
> > because those checks are done higher in the stack.
>
> After taking a closer look at the checks in do_fallocate(), I don't know
> that this statement is correct. The sanity checks around offset, len,
> and mode aren't guaranteed to be done higher up in the stack. The
> existing VFS helper functions also seem to do these types of checks. I
> think the rest of the checks are redundant.
I obviously goofed up here. Thieu states where offset and len are
checked in his following sentence. Not sure how I missed that. My
apologies.
However, I do still think that we need the fallocate mode checks in
vfs_fallocate().
Tyler
> > Checking of offset and
> > len are done by rw_verify_area() and generic_write_checks(). These
> > functions are called by VFS before ecryptfs invokes vfs_fallocate() in its
> > ecryptfs_write_end() function. And since ecryptfs directly opens the lower
> > file, it ensures that the file is opened with the proper flags and mode.
> >
> > Signed-off-by: Thieu Le <thieule@xxxxxxxxxxxx>
> > ---
> > fs/open.c | 14 ++++++++++----
> > include/linux/fs.h | 2 ++
> > 2 files changed, 12 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/open.c b/fs/open.c
> > index f711921..8a4ba20 100644
> > --- a/fs/open.c
> > +++ b/fs/open.c
> > @@ -214,6 +214,15 @@ SYSCALL_ALIAS(sys_ftruncate64, SyS_ftruncate64);
> > #endif /* BITS_PER_LONG == 32 */
> >
> >
> > +int vfs_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
> > +{
> > + if (!file->f_op->fallocate)
> > + return -EOPNOTSUPP;
> > +
> > + return file->f_op->fallocate(file, mode, offset, len);
> > +}
> > +EXPORT_SYMBOL(vfs_fallocate);
> > +
> > int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
> > {
> > struct inode *inode = file->f_path.dentry->d_inode;
> > @@ -263,10 +272,7 @@ int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
> > if (((offset + len) > inode->i_sb->s_maxbytes) || ((offset + len) < 0))
> > return -EFBIG;
> >
> > - if (!file->f_op->fallocate)
> > - return -EOPNOTSUPP;
> > -
> > - return file->f_op->fallocate(file, mode, offset, len);
> > + return vfs_fallocate(file, mode, offset, len);
> > }
> >
> > SYSCALL_DEFINE(fallocate)(int fd, int mode, loff_t offset, loff_t len)
> > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > index 277f497..c0e1225 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -1504,6 +1504,8 @@ extern int vfs_link(struct dentry *, struct inode *, struct dentry *);
> > extern int vfs_rmdir(struct inode *, struct dentry *);
> > extern int vfs_unlink(struct inode *, struct dentry *);
> > extern int vfs_rename(struct inode *, struct dentry *, struct inode *, struct dentry *);
> > +extern int vfs_fallocate(struct file *file, int mode, loff_t offset,
> > + loff_t len);
> >
> > /*
> > * VFS dentry helper functions.
> > --
> > 1.7.3.1
> >
> > --
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