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Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <20230519074047.1739879-1-dhowells@redhat.com> <20230519074047.1739879-4-dhowells@redhat.com> <1742093.1684485814@warthog.procyon.org.uk> To: Christoph Hellwig Cc: dhowells@redhat.com, Jens Axboe , Al Viro , Matthew Wilcox , Jan Kara , Jeff Layton , David Hildenbrand , Jason Gunthorpe , Logan Gunthorpe , Hillf Danton , Christian Brauner , Linus Torvalds , linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Christoph Hellwig Subject: Re: [PATCH v20 03/32] splice: Make direct_read_splice() limit to eof where appropriate MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <2154517.1684535271.1@warthog.procyon.org.uk> Content-Transfer-Encoding: quoted-printable Date: Fri, 19 May 2023 23:27:51 +0100 Message-ID: <2154518.1684535271@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 X-Rspamd-Queue-Id: E7CB040012 X-Rspam-User: X-Stat-Signature: fq7uc5a9skqjdubtj1n9snhdp3aoi61e X-Rspamd-Server: rspam01 X-HE-Tag: 1684535279-769366 X-HE-Meta: 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 0/i3oTpR c6oTWwLv3OHaX6vcG0SphznzTFpbDyqmd8UIE52uB4XtQvFkryBnfvjKvQ6NyjnIFIMTcWrzFiuAPFHTqzoIsn4lINpn0cBh8J5eOJGnRmxBNDWAnhYjh1W9hQMDr87Gs7fZL4F5i0oGAdLCdsMIZcU/r+J62JQrV4NTF1alRRdDTzKmFmtdru/pZbG/XNgpN36PmBpaOIq3Mu5A= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Okay. Let's go with that. So I have to put the handling in vfs_splice_re= ad(): long vfs_splice_read(struct file *in, loff_t *ppos, struct pipe_inode_info *pipe, size_t len, unsigned int flags) { ... if (unlikely(!in->f_op->splice_read)) return warn_unsupported(in, "read"); /* * O_DIRECT and DAX don't deal with the pagecache, so we * allocate a buffer, copy into it and splice that into the pipe. */ if ((in->f_flags & O_DIRECT) || IS_DAX(in->f_mapping->host)) return copy_splice_read(in, ppos, pipe, len, flags); return in->f_op->splice_read(in, ppos, pipe, len, flags); } which leaves very little in generic_file_splice_read: ssize_t generic_file_splice_read(struct file *in, loff_t *ppos, struct pipe_inode_info *pipe, size_t len, unsigned int flags) { if (unlikely(*ppos >=3D in->f_mapping->host->i_sb->s_maxbytes)) return 0; if (unlikely(!len)) return 0; return filemap_splice_read(in, ppos, pipe, len, flags); } so I wonder if the tests in generic_file_splice_read() can be folded into vfs_splice_read(), pointers to generic_file_splice_read() be replaced with pointers to filemap_splice_read() and generic_file_splice_read() just be removed. I suspect we can't quite do this because of the *ppos check - but I wonder= if that's actually necessary since filemap_splice_read() checks against i_size... or if the check can be moved there if we definitely want to do i= t. Certainly, the zero-length check can be done in vfs_splice_read(). David