From: jlayton@kernel.org To: Andrew Morton <akpm@linux-foundation.org>, Al Viro <viro@ZenIV.linux.org.uk>, Jan Kara <jack@suse.cz>, tytso@mit.edu, axboe@kernel.dk, mawilcox@microsoft.com, ross.zwisler@linux.intel.com, corbet@lwn.net, Chris Mason <clm@fb.com>, Josef Bacik <jbacik@fb.com>, David Sterba <dsterba@suse.com>, "Darrick J . Wong" <darrick.wong@oracle.com> Cc: Carlos Maiolino <cmaiolino@redhat.com>, Eryu Guan <eguan@redhat.com>, David Howells <dhowells@redhat.com>, Christoph Hellwig <hch@infradead.org>, Liu Bo <bo.li.liu@oracle.com>, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-block@vger.kernel.org Subject: [PATCH v8 12/18] Documentation: flesh out the section in vfs.txt on storing and reporting writeback errors Date: Thu, 29 Jun 2017 09:19:48 -0400 [thread overview] Message-ID: <20170629131954.28733-13-jlayton@kernel.org> (raw) In-Reply-To: <20170629131954.28733-1-jlayton@kernel.org> From: Jeff Layton <jlayton@redhat.com> Let's try to make this extra clear for fs authors. Cc: Jan Kara <jack@suse.cz> Signed-off-by: Jeff Layton <jlayton@redhat.com> --- Documentation/filesystems/vfs.txt | 43 ++++++++++++++++++++++++++++++++++++--- 1 file changed, 40 insertions(+), 3 deletions(-) diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt index f42b90687d40..1366043b3942 100644 --- a/Documentation/filesystems/vfs.txt +++ b/Documentation/filesystems/vfs.txt @@ -576,7 +576,42 @@ should clear PG_Dirty and set PG_Writeback. It can be actually written at any point after PG_Dirty is clear. Once it is known to be safe, PG_Writeback is cleared. -Writeback makes use of a writeback_control structure... +Writeback makes use of a writeback_control structure to direct the +operations. This gives the the writepage and writepages operations some +information about the nature of and reason for the writeback request, +and the constraints under which it is being done. It is also used to +return information back to the caller about the result of a writepage or +writepages request. + +Handling errors during writeback +-------------------------------- +Most applications that utilize the pagecache will periodically call +fsync to ensure that data written has made it to the backing store. +When there is an error during writeback, they expect that error to be +reported when fsync is called. After an error has been reported on one +fsync, subsequent fsync calls on the same file descriptor should return +0, unless further writeback errors have occurred since the previous +fsync. + +Ideally, the kernel would report an error only on file descriptions on +which writes were done that subsequently failed to be written back. The +generic pagecache infrastructure does not track the file descriptions +that have dirtied each individual page however, so determining which +file descriptors should get back an error is not possible. + +Instead, the generic writeback error tracking infrastructure in the +kernel settles for reporting errors to fsync on all file descriptions +that were open at the time that the error occurred. In a situation with +multiple writers, all of them will get back an error on a subsequent fsync, +even if all of the writes done through that particular file descriptor +succeeded (or even if there were no writes on that file descriptor at all). + +Filesystems that wish to use this infrastructure should call +mapping_set_error to record the error in the address_space when it +occurs. Then, at the end of their fsync operation, they should call +file_check_and_advance_wb_err to ensure that the struct file's error +cursor has advanced to the correct point in the stream of errors emitted +by the backing device(s). struct address_space_operations ------------------------------- @@ -804,7 +839,8 @@ struct address_space_operations { The File Object =============== -A file object represents a file opened by a process. +A file object represents a file opened by a process. This is also known +as an "open file description" in POSIX parlance. struct file_operations @@ -887,7 +923,8 @@ otherwise noted. release: called when the last reference to an open file is closed - fsync: called by the fsync(2) system call + fsync: called by the fsync(2) system call. Also see the section above + entitled "Handling errors during writeback". fasync: called by the fcntl(2) system call when asynchronous (non-blocking) mode is enabled for a file -- 2.13.0
WARNING: multiple messages have this Message-ID (diff)
From: jlayton@kernel.org To: Andrew Morton <akpm@linux-foundation.org>, Al Viro <viro@ZenIV.linux.org.uk>, Jan Kara <jack@suse.cz>, tytso@mit.edu, axboe@kernel.dk, mawilcox@microsoft.com, ross.zwisler@linux.intel.com, corbet@lwn.net, Chris Mason <clm@fb.com>, Josef Bacik <jbacik@fb.com>, David Sterba <dsterba@suse.com>, "Darrick J . Wong" <darrick.wong@oracle.com> Cc: Carlos Maiolino <cmaiolino@redhat.com>, Eryu Guan <eguan@redhat.com>, David Howells <dhowells@redhat.com>, Christoph Hellwig <hch@infradead.org>, Liu Bo <bo.li.liu@oracle.com>, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-block@vger.kernel.org Subject: [PATCH v8 12/18] Documentation: flesh out the section in vfs.txt on storing and reporting writeback errors Date: Thu, 29 Jun 2017 09:19:48 -0400 [thread overview] Message-ID: <20170629131954.28733-13-jlayton@kernel.org> (raw) In-Reply-To: <20170629131954.28733-1-jlayton@kernel.org> From: Jeff Layton <jlayton@redhat.com> Let's try to make this extra clear for fs authors. Cc: Jan Kara <jack@suse.cz> Signed-off-by: Jeff Layton <jlayton@redhat.com> --- Documentation/filesystems/vfs.txt | 43 ++++++++++++++++++++++++++++++++++++--- 1 file changed, 40 insertions(+), 3 deletions(-) diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt index f42b90687d40..1366043b3942 100644 --- a/Documentation/filesystems/vfs.txt +++ b/Documentation/filesystems/vfs.txt @@ -576,7 +576,42 @@ should clear PG_Dirty and set PG_Writeback. It can be actually written at any point after PG_Dirty is clear. Once it is known to be safe, PG_Writeback is cleared. -Writeback makes use of a writeback_control structure... +Writeback makes use of a writeback_control structure to direct the +operations. This gives the the writepage and writepages operations some +information about the nature of and reason for the writeback request, +and the constraints under which it is being done. It is also used to +return information back to the caller about the result of a writepage or +writepages request. + +Handling errors during writeback +-------------------------------- +Most applications that utilize the pagecache will periodically call +fsync to ensure that data written has made it to the backing store. +When there is an error during writeback, they expect that error to be +reported when fsync is called. After an error has been reported on one +fsync, subsequent fsync calls on the same file descriptor should return +0, unless further writeback errors have occurred since the previous +fsync. + +Ideally, the kernel would report an error only on file descriptions on +which writes were done that subsequently failed to be written back. The +generic pagecache infrastructure does not track the file descriptions +that have dirtied each individual page however, so determining which +file descriptors should get back an error is not possible. + +Instead, the generic writeback error tracking infrastructure in the +kernel settles for reporting errors to fsync on all file descriptions +that were open at the time that the error occurred. In a situation with +multiple writers, all of them will get back an error on a subsequent fsync, +even if all of the writes done through that particular file descriptor +succeeded (or even if there were no writes on that file descriptor at all). + +Filesystems that wish to use this infrastructure should call +mapping_set_error to record the error in the address_space when it +occurs. Then, at the end of their fsync operation, they should call +file_check_and_advance_wb_err to ensure that the struct file's error +cursor has advanced to the correct point in the stream of errors emitted +by the backing device(s). struct address_space_operations ------------------------------- @@ -804,7 +839,8 @@ struct address_space_operations { The File Object =============== -A file object represents a file opened by a process. +A file object represents a file opened by a process. This is also known +as an "open file description" in POSIX parlance. struct file_operations @@ -887,7 +923,8 @@ otherwise noted. release: called when the last reference to an open file is closed - fsync: called by the fsync(2) system call + fsync: called by the fsync(2) system call. Also see the section above + entitled "Handling errors during writeback". fasync: called by the fcntl(2) system call when asynchronous (non-blocking) mode is enabled for a file -- 2.13.0 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2017-06-29 13:19 UTC|newest] Thread overview: 90+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-06-29 13:19 [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1) jlayton 2017-06-29 13:19 ` jlayton 2017-06-29 13:19 ` [PATCH v8 01/18] fs: remove call_fsync helper function jlayton 2017-06-29 13:19 ` jlayton 2017-06-29 13:19 ` [PATCH v8 02/18] buffer: use mapping_set_error instead of setting the flag jlayton 2017-06-29 13:19 ` jlayton 2017-06-29 13:19 ` [PATCH v8 03/18] fs: check for writeback errors after syncing out buffers in generic_file_fsync jlayton 2017-06-29 13:19 ` jlayton 2017-06-29 14:19 ` Christoph Hellwig 2017-06-29 14:19 ` Christoph Hellwig 2017-06-29 20:17 ` Jeff Layton 2017-06-29 20:17 ` Jeff Layton 2017-06-29 20:17 ` Jeff Layton 2017-06-29 20:17 ` Jeff Layton 2017-06-29 13:19 ` [PATCH v8 04/18] buffer: set errors in mapping at the time that the error occurs jlayton 2017-06-29 13:19 ` jlayton 2017-06-29 13:19 ` [PATCH v8 05/18] jbd2: don't clear and reset errors after waiting on writeback jlayton 2017-06-29 13:19 ` jlayton 2017-06-29 13:19 ` [PATCH v8 06/18] mm: clear AS_EIO/AS_ENOSPC when writeback initiation fails jlayton 2017-06-29 13:19 ` jlayton 2017-06-29 13:19 ` [PATCH v8 07/18] mm: don't TestClearPageError in __filemap_fdatawait_range jlayton 2017-06-29 13:19 ` jlayton 2017-06-29 13:19 ` [PATCH v8 08/18] mm: clean up error handling in write_one_page jlayton 2017-06-29 13:19 ` jlayton 2017-06-29 13:19 ` [PATCH v8 09/18] lib: add errseq_t type and infrastructure for handling it jlayton 2017-06-29 13:19 ` jlayton 2017-06-29 13:19 ` [PATCH v8 10/18] fs: new infrastructure for writeback error handling and reporting jlayton 2017-06-29 13:19 ` jlayton 2017-06-29 13:45 ` Jeff Layton 2017-06-29 13:45 ` Jeff Layton 2017-06-29 13:45 ` Jeff Layton 2017-06-29 13:45 ` Jeff Layton 2017-06-29 17:52 ` Jeff Layton 2017-06-29 17:52 ` Jeff Layton 2017-06-29 17:52 ` Jeff Layton 2017-06-29 17:52 ` Jeff Layton 2017-06-29 13:19 ` [PATCH v8 11/18] mm: set both AS_EIO/AS_ENOSPC and errseq_t in mapping_set_error jlayton 2017-06-29 13:19 ` jlayton 2017-06-29 13:19 ` jlayton [this message] 2017-06-29 13:19 ` [PATCH v8 12/18] Documentation: flesh out the section in vfs.txt on storing and reporting writeback errors jlayton 2017-06-29 17:11 ` Darrick J. Wong 2017-06-29 17:11 ` Darrick J. Wong 2017-06-29 18:13 ` Jeff Layton 2017-06-29 18:13 ` Jeff Layton 2017-06-29 18:13 ` Jeff Layton 2017-06-29 18:13 ` Jeff Layton 2017-06-29 18:21 ` Matthew Wilcox 2017-06-29 18:21 ` Matthew Wilcox 2017-06-29 18:21 ` Matthew Wilcox 2017-06-29 20:42 ` Jeff Layton 2017-06-29 20:42 ` Jeff Layton 2017-06-29 20:42 ` Jeff Layton 2017-06-29 20:42 ` Jeff Layton 2017-06-29 20:42 ` Jeff Layton 2017-06-29 13:19 ` [PATCH v8 13/18] dax: set errors in mapping when writeback fails jlayton 2017-06-29 13:19 ` jlayton 2017-06-29 13:19 ` [PATCH v8 14/18] block: convert to errseq_t based writeback error tracking jlayton 2017-06-29 13:19 ` jlayton 2017-06-29 14:18 ` Christoph Hellwig 2017-06-29 14:18 ` Christoph Hellwig 2017-06-29 13:19 ` [PATCH v8 15/18] fs: convert __generic_file_fsync to use errseq_t based reporting jlayton 2017-06-29 13:19 ` jlayton 2017-06-29 13:19 ` [PATCH v8 16/18] ext4: use errseq_t based error handling for reporting data writeback errors jlayton 2017-06-29 13:19 ` jlayton 2017-06-29 14:12 ` Christoph Hellwig 2017-06-29 14:12 ` Christoph Hellwig 2017-06-29 20:26 ` Jeff Layton 2017-06-29 20:26 ` Jeff Layton 2017-06-29 20:26 ` Jeff Layton 2017-06-29 20:26 ` Jeff Layton 2017-06-29 13:19 ` [PATCH v8 17/18] xfs: minimal conversion to errseq_t writeback error reporting jlayton 2017-06-29 13:19 ` jlayton 2017-06-29 14:12 ` Christoph Hellwig 2017-06-29 14:12 ` Christoph Hellwig 2017-06-30 16:45 ` Jeff Layton 2017-06-30 16:45 ` Jeff Layton 2017-06-30 16:45 ` Jeff Layton 2017-06-30 16:45 ` Jeff Layton 2017-06-30 16:49 ` Christoph Hellwig 2017-06-30 16:49 ` Christoph Hellwig 2017-06-29 17:13 ` Darrick J. Wong 2017-06-29 17:13 ` Darrick J. Wong 2017-06-29 13:19 ` [PATCH v8 18/18] btrfs: minimal conversion to errseq_t writeback error reporting on fsync jlayton 2017-06-29 13:19 ` jlayton 2017-06-29 14:17 ` Christoph Hellwig 2017-06-29 14:17 ` Christoph Hellwig 2017-06-29 20:32 ` Jeff Layton 2017-06-29 20:32 ` Jeff Layton 2017-06-29 20:32 ` Jeff Layton 2017-06-29 20:32 ` Jeff Layton
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