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Date: Fri, 3 May 2019 08:35:06 -0400
From: Amir Goldstein <amir73il@...il.com>
To: Stephen Rothwell <sfr@...b.auug.org.au>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Jens Axboe <axboe@...nel.dk>,
Linux Next Mailing List <linux-next@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: linux-next: manual merge of the akpm-current tree with the block tree
On Fri, May 3, 2019 at 5:10 AM Stephen Rothwell <sfr@...b.auug.org.au> wrote:
>
> Hi all,
>
> Today's linux-next merge of the akpm-current tree got a conflict in:
>
> fs/sync.c
>
> between commit:
>
> 22f96b3808c1 ("fs: add sync_file_range() helper")
>
> from the block tree and commit:
>
> 9a8d18789a18 ("fs/sync.c: sync_file_range(2) may use WB_SYNC_ALL writeback")
>
> from the akpm-current tree.
>
> I fixed it up (see below) and can carry the fix as necessary. This
> is now fixed as far as linux-next is concerned, but any non trivial
> conflicts should be mentioned to your upstream maintainer when your tree
> is submitted for merging. You may also want to consider cooperating
> with the maintainer of the conflicting tree to minimise any particularly
> complex conflicts.
>
Fix looks technically correct, but it would have been better if the fat
comment moved to the fat helper and then replace
s/sys_sync_file_range/ksys_sync_file_range with
s/sys_sync_file_range/sync_file_range
It is probably best if either maintainer took both patches through his tree
and if move and update the comment from "sys_sync_file_range" be done
as part of the helper function patch.
Thanks,
Amir.
> --
> Cheers,
> Stephen Rothwell
>
> diff --cc fs/sync.c
> index 01e82170545a,9e8cd90e890f..000000000000
> --- a/fs/sync.c
> +++ b/fs/sync.c
> @@@ -292,10 -348,16 +292,16 @@@ int sync_file_range(struct file *file,
> }
>
> if (flags & SYNC_FILE_RANGE_WRITE) {
> + int sync_mode = WB_SYNC_NONE;
> +
> + if ((flags & SYNC_FILE_RANGE_WRITE_AND_WAIT) ==
> + SYNC_FILE_RANGE_WRITE_AND_WAIT)
> + sync_mode = WB_SYNC_ALL;
> +
> ret = __filemap_fdatawrite_range(mapping, offset, endbyte,
> - WB_SYNC_NONE);
> + sync_mode);
> if (ret < 0)
> - goto out_put;
> + goto out;
> }
>
> if (flags & SYNC_FILE_RANGE_WAIT_AFTER)
> @@@ -305,68 -369,6 +311,71 @@@ out
> return ret;
> }
>
> +/*
> - * sys_sync_file_range() permits finely controlled syncing over a segment of
> ++ * ksys_sync_file_range() permits finely controlled syncing over a segment of
> + * a file in the range offset .. (offset+nbytes-1) inclusive. If nbytes is
> - * zero then sys_sync_file_range() will operate from offset out to EOF.
> ++ * zero then ksys_sync_file_range() will operate from offset out to EOF.
> + *
> + * The flag bits are:
> + *
> + * SYNC_FILE_RANGE_WAIT_BEFORE: wait upon writeout of all pages in the range
> + * before performing the write.
> + *
> + * SYNC_FILE_RANGE_WRITE: initiate writeout of all those dirty pages in the
> + * range which are not presently under writeback. Note that this may block for
> + * significant periods due to exhaustion of disk request structures.
> + *
> + * SYNC_FILE_RANGE_WAIT_AFTER: wait upon writeout of all pages in the range
> + * after performing the write.
> + *
> + * Useful combinations of the flag bits are:
> + *
> + * SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE: ensures that all pages
> - * in the range which were dirty on entry to sys_sync_file_range() are placed
> ++ * in the range which were dirty on entry to ksys_sync_file_range() are placed
> + * under writeout. This is a start-write-for-data-integrity operation.
> + *
> + * SYNC_FILE_RANGE_WRITE: start writeout of all dirty pages in the range which
> + * are not presently under writeout. This is an asynchronous flush-to-disk
> + * operation. Not suitable for data integrity operations.
> + *
> + * SYNC_FILE_RANGE_WAIT_BEFORE (or SYNC_FILE_RANGE_WAIT_AFTER): wait for
> + * completion of writeout of all pages in the range. This will be used after an
> + * earlier SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE operation to wait
> + * for that operation to complete and to return the result.
> + *
> - * SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE|SYNC_FILE_RANGE_WAIT_AFTER:
> ++ * SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE|SYNC_FILE_RANGE_WAIT_AFTER
> ++ * (a.k.a. SYNC_FILE_RANGE_WRITE_AND_WAIT):
> + * a traditional sync() operation. This is a write-for-data-integrity operation
> + * which will ensure that all pages in the range which were dirty on entry to
> - * sys_sync_file_range() are committed to disk.
> ++ * ksys_sync_file_range() are committed to disk. It should be noted that disk
> ++ * caches are not flushed by this call, so there are no guarantees here that the
> ++ * data will be available on disk after a crash.
> + *
> + *
> + * SYNC_FILE_RANGE_WAIT_BEFORE and SYNC_FILE_RANGE_WAIT_AFTER will detect any
> + * I/O errors or ENOSPC conditions and will return those to the caller, after
> + * clearing the EIO and ENOSPC flags in the address_space.
> + *
> + * It should be noted that none of these operations write out the file's
> + * metadata. So unless the application is strictly performing overwrites of
> + * already-instantiated disk blocks, there are no guarantees here that the data
> + * will be available after a crash.
> + */
> +int ksys_sync_file_range(int fd, loff_t offset, loff_t nbytes,
> + unsigned int flags)
> +{
> + int ret;
> + struct fd f;
> +
> + ret = -EBADF;
> + f = fdget(fd);
> + if (f.file)
> + ret = sync_file_range(f.file, offset, nbytes, flags);
> +
> + fdput(f);
> + return ret;
> +}
> +
> SYSCALL_DEFINE4(sync_file_range, int, fd, loff_t, offset, loff_t, nbytes,
> unsigned int, flags)
> {
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