On Thursday 01 Oct 2015 10:57:52 Josef Bacik wrote:
> On 09/30/2015 06:28 AM, Chandan Rajendra wrote:
> > When extending a file by either "truncate up" or by writing beyond i_size,
> > the page which had i_size needs to be marked "read only" so that future
> > writes to the page via mmap interface causes btrfs_page_mkwrite() to be
> > invoked. If not, a write performed after extending the file via the mmap
> > interface will find the page to be writaeable and continue writing to the
> > page without invoking btrfs_page_mkwrite() i.e. we end up writing to a
> > file without reserving disk space.
> >
> > Signed-off-by: Chandan Rajendra <chandan@xxxxxxxxxxxxxxxxxx>
> > ---
> >
> > fs/btrfs/file.c | 12 ++++++++++--
> > fs/btrfs/inode.c | 2 +-
> > 2 files changed, 11 insertions(+), 3 deletions(-)
> >
> > diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> > index 360d56d..5715e29 100644
> > --- a/fs/btrfs/file.c
> > +++ b/fs/btrfs/file.c
> > @@ -1757,6 +1757,8 @@ static ssize_t btrfs_file_write_iter(struct kiocb
> > *iocb,>
> > ssize_t err;
> > loff_t pos;
> > size_t count;
> >
> > + loff_t oldsize;
> > + int clean_page = 0;
> >
> > mutex_lock(&inode->i_mutex);
> > err = generic_write_checks(iocb, from);
> >
> > @@ -1795,14 +1797,17 @@ static ssize_t btrfs_file_write_iter(struct kiocb
> > *iocb,>
> > pos = iocb->ki_pos;
> > count = iov_iter_count(from);
> > start_pos = round_down(pos, root->sectorsize);
> >
> > - if (start_pos > i_size_read(inode)) {
> > + oldsize = i_size_read(inode);
> > + if (start_pos > oldsize) {
> >
> > /* Expand hole size to cover write data, preventing empty gap
*/
> > end_pos = round_up(pos + count, root->sectorsize);
> >
> > - err = btrfs_cont_expand(inode, i_size_read(inode), end_pos);
> > + err = btrfs_cont_expand(inode, oldsize, end_pos);
> >
> > if (err) {
> >
> > mutex_unlock(&inode->i_mutex);
> > goto out;
> >
> > }
> >
> > + if (start_pos > round_up(oldsize, root->sectorsize))
> > + clean_page = 1;
> >
> > }
> >
> > if (sync)
> >
> > @@ -1814,6 +1819,9 @@ static ssize_t btrfs_file_write_iter(struct kiocb
> > *iocb,>
> > num_written = __btrfs_buffered_write(file, from, pos);
> > if (num_written > 0)
> >
> > iocb->ki_pos = pos + num_written;
> >
> > + if (clean_page)
> > + pagecache_isize_extended(inode, oldsize,
> > + i_size_read(inode));
> >
> > }
> >
> > mutex_unlock(&inode->i_mutex);
> >
> > diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> > index c937357..f31da87 100644
> > --- a/fs/btrfs/inode.c
> > +++ b/fs/btrfs/inode.c
> > @@ -4853,7 +4853,6 @@ static int btrfs_setsize(struct inode *inode, struct
> > iattr *attr)>
> > }
> >
> > if (newsize > oldsize) {
> >
> > - truncate_pagecache(inode, newsize);
>
> So I don't understand why we are dropping this bit here, could you
> explain? Otherwise the patch looks fine to me. Thanks,
>
Josef, As per our previous discussion on IRC we found that the
"truncate_pagecache(inode, newsize)" statement to be a relic of the
past. During the test runs, I haven't seen any sort of failure caused by the
removal of this statement.
--
chandan
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