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Message-ID: <20170610052703.GC6365@ZenIV.linux.org.uk> Date: Sat, 10 Jun 2017 06:27:03 +0100 From: Al Viro <viro@...IV.linux.org.uk> To: Goldwyn Rodrigues <rgoldwyn@...e.de> Cc: linux-fsdevel@...r.kernel.org, jack@...e.com, hch@...radead.org, linux-block@...r.kernel.org, linux-btrfs@...r.kernel.org, linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org, axboe@...nel.dk, linux-api@...r.kernel.org, adam.manzanares@....com, Goldwyn Rodrigues <rgoldwyn@...e.com> Subject: Re: [PATCH 04/10] fs: Introduce RWF_NOWAIT On Tue, Jun 06, 2017 at 06:19:33AM -0500, Goldwyn Rodrigues wrote: > From: Goldwyn Rodrigues <rgoldwyn@...e.com> > > RWF_NOWAIT informs kernel to bail out if an AIO request will block > for reasons such as file allocations, or a writeback triggered, > or would block while allocating requests while performing > direct I/O. > > RWF_NOWAIT is translated to IOCB_NOWAIT for iocb->ki_flags. > > The check for -EOPNOTSUPP is placed in generic_file_write_iter(). This > is called by most filesystems, either through fsops.write_iter() or through > the function defined by write_iter(). If not, we perform the check defined > by .write_iter() which is called for direct IO specifically. > > Filesystems xfs, btrfs and ext4 would be supported in the following patches. Umm... What about ->write_iter() instances outside of fs/*? Even in fs/*, consider e.g. int cifs_get_writer(struct cifsInodeInfo *cinode) { int rc; start: rc = wait_on_bit(&cinode->flags, CIFS_INODE_PENDING_OPLOCK_BREAK, TASK_KILLABLE); and cifs_file_write_iter() calling it before going to generic_file_write_iter(). Ditto for cifs_struct_writev()... coda_file_write_iter() does inode_lock() before calling vfs_iter_write(). ext2_dax_write_iter(): inode_lock(). f2fs_file_write_iter(): ditto. fuse_file_write_iter(): ditto in case when ->writeback_cache is false. gfs2 is O_APPEND case: almost certainly blocks. ncp_file_write_iter(): blocks (mutex_lock(&NCP_FINFO(inode)->open_mutex) in ncp_make_open(), not to mention anything else). ntfs_file_write_iter(): inode_lock(). orangefs_file_write_iter(): ditto. ubifs_write_iter(): may block in update_mctime(). udf_file_write_iter(): inode_lock(). Lustre sure as hell does block before it gets anywhere near mm/filemap.c. And that - just from looking at regular files. Then we have sockets and pipes, not to mention weird stuff like fs/fuse/cuse.c, etc.
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