From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D430DC3F2D3 for ; Sat, 29 Feb 2020 18:11:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9AB1320661 for ; Sat, 29 Feb 2020 18:11:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=osandov-com.20150623.gappssmtp.com header.i=@osandov-com.20150623.gappssmtp.com header.b="boYMWy0u" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727473AbgB2SLA (ORCPT ); Sat, 29 Feb 2020 13:11:00 -0500 Received: from mail-pl1-f195.google.com ([209.85.214.195]:44352 "EHLO mail-pl1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727366AbgB2SLA (ORCPT ); Sat, 29 Feb 2020 13:11:00 -0500 Received: by mail-pl1-f195.google.com with SMTP id d9so2527029plo.11 for ; Sat, 29 Feb 2020 10:10:57 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=osandov-com.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=7sy8AOJ/15eT2KVP4UWt2JpZHRiEAQnmxmL1o6lYero=; b=boYMWy0uH+IGGQmZ9jR9o/oMeVuC1J2Vk0aQ4D2AJNgzv3nUtfC9EIbHaRI6i34gPM SbkrlyvZArKyc4DPoNXiYhlrvZn5dJNu4CfnBhWX901WWM9vTpB3uBlLfW5jbtWrSjyo eo4HOrEdyMyaUzvNWnK9V9mTH1+ZoBKjbNRfBGDx2In7lCAptkh5Uv2tyolS0IgUm4cR gXzx3q2/uy3u//9LAxtkRuVB8T3qFjf9e2w/FoBBawSCIHs2k3Q1i+pN7Dbza8GvyuC/ JXZFYjEtriuIs7gT4que4PlLtylT4e6HTqDLfvao16GrS3JequXyBMiemXgY+d8lXe6A DBMA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=7sy8AOJ/15eT2KVP4UWt2JpZHRiEAQnmxmL1o6lYero=; b=CwRXBbI2U+rhRC6Yy7JrE1CcZ3IIY+WGqwwRim6oKvxyxWpbm5tdvaD4i9Y/7e/Doi /K8/HJ3j1Mn294IcohpSe3cwW2nRk7Nm7+zOt6foLJLQ3omERYTzTvSFMZ/Dq8OiESid PByxHYbLWouqvYSIXu69uBgrZ3lUF1p/3FKmtyEi9f4i+Jrp3vEM/T8SsBIwFCxNAepW Ve5jbvmrbsbYj3e7HKfInaeDgmhJShIJ0Ol8vnMo8fH8zrEdrJ+qXGBZVko8zcs94cEz ISyzvXblZTffi8xtMVxaPM2++V+ESdczOSgd9LSEtymp3eihUHn/aLrB4/8NiQJUCTRG 1Qtg== X-Gm-Message-State: APjAAAWsdwWy3PZrwacqDOGMS3lQIHNTz1ENDw/RPSMSOpp62yYbRO4B YKZLGWN4mjGgNaqldtsMxBIZ3Q== X-Google-Smtp-Source: APXvYqybeS5MbSric+KrWp1UODE4dnY4mGpqShiZFnfzfg5BetSTd/rk0guzRj9/e465cj5luyQuQw== X-Received: by 2002:a17:902:be04:: with SMTP id r4mr9771281pls.315.1582999857094; Sat, 29 Feb 2020 10:10:57 -0800 (PST) Received: from vader ([2607:fb90:8365:d596:e6a7:a0ff:fe0b:c9a8]) by smtp.gmail.com with ESMTPSA id l37sm6283692pjb.15.2020.02.29.10.10.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 29 Feb 2020 10:10:56 -0800 (PST) Date: Sat, 29 Feb 2020 10:10:53 -0800 From: Omar Sandoval To: Amir Goldstein Cc: linux-fsdevel , Linux Btrfs , Al Viro , Christoph Hellwig , Dave Chinner , Jann Horn , Aleksa Sarai , Linux API , kernel-team@fb.com Subject: Re: [PATCH v4 3/9] fs: add RWF_ENCODED for reading/writing compressed data Message-ID: <20200229181053.GB157744@vader> References: <4f8b9a66f5f6efdb9cab566581acb292f0b5b528.1582930832.git.osandov@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Sat, Feb 29, 2020 at 12:40:58PM +0200, Amir Goldstein wrote: > On Sat, Feb 29, 2020 at 1:14 AM Omar Sandoval wrote: > > > > From: Omar Sandoval > > > > Btrfs supports transparent compression: data written by the user can be > > compressed when written to disk and decompressed when read back. > > However, we'd like to add an interface to write pre-compressed data > > directly to the filesystem, and the matching interface to read > > compressed data without decompressing it. This adds support for > > so-called "encoded I/O" via preadv2() and pwritev2(). > > > > A new RWF_ENCODED flags indicates that a read or write is "encoded". If > > this flag is set, iov[0].iov_base points to a struct encoded_iov which > > is used for metadata: namely, the compression algorithm, unencoded > > (i.e., decompressed) length, and what subrange of the unencoded data > > should be used (needed for truncated or hole-punched extents and when > > reading in the middle of an extent). For reads, the filesystem returns > > this information; for writes, the caller provides it to the filesystem. > > iov[0].iov_len must be set to sizeof(struct encoded_iov), which can be > > used to extend the interface in the future a la copy_struct_from_user(). > > The remaining iovecs contain the encoded extent. > > > > This adds the VFS helpers for supporting encoded I/O and documentation > > for filesystem support. > > > > Signed-off-by: Omar Sandoval > > --- > > Documentation/filesystems/encoded_io.rst | 74 ++++++++++ > > Documentation/filesystems/index.rst | 1 + > > include/linux/fs.h | 16 +++ > > include/uapi/linux/fs.h | 33 ++++- > > mm/filemap.c | 166 +++++++++++++++++++++-- > > 5 files changed, 276 insertions(+), 14 deletions(-) > > create mode 100644 Documentation/filesystems/encoded_io.rst > > > > diff --git a/Documentation/filesystems/encoded_io.rst b/Documentation/filesystems/encoded_io.rst > > new file mode 100644 > > index 000000000000..50405276d866 > > --- /dev/null > > +++ b/Documentation/filesystems/encoded_io.rst > > @@ -0,0 +1,74 @@ > > +=========== > > +Encoded I/O > > +=========== > > + > > +Encoded I/O is a mechanism for reading and writing encoded (e.g., compressed > > +and/or encrypted) data directly from/to the filesystem. The userspace interface > > +is thoroughly described in the :manpage:`encoded_io(7)` man page; this document > > +describes the requirements for filesystem support. > > + > > +First of all, a filesystem supporting encoded I/O must indicate this by setting > > +the ``FMODE_ENCODED_IO`` flag in its ``file_open`` file operation:: > > + > > + static int foo_file_open(struct inode *inode, struct file *filp) > > + { > > + ... > > + filep->f_mode |= FMODE_ENCODED_IO; > > + ... > > + } > > + > > +Encoded I/O goes through ``read_iter`` and ``write_iter``, designated by the > > +``IOCB_ENCODED`` flag in ``kiocb->ki_flags``. > > + > > +Reads > > +===== > > + > > +Encoded ``read_iter`` should: > > + > > +1. Call ``generic_encoded_read_checks()`` to validate the file and buffers > > + provided by userspace. > > +2. Initialize the ``encoded_iov`` appropriately. > > +3. Copy it to the user with ``copy_encoded_iov_to_iter()``. > > +4. Copy the encoded data to the user. > > +5. Advance ``kiocb->ki_pos`` by ``encoded_iov->len``. > > +6. Return the size of the encoded data read, not including the ``encoded_iov``. > > + > > +There are a few details to be aware of: > > + > > +* Encoded ``read_iter`` should support reading unencoded data if the extent is > > + not encoded. > > +* If the buffers provided by the user are not large enough to contain an entire > > + encoded extent, then ``read_iter`` should return ``-ENOBUFS``. This is to > > + avoid confusing userspace with truncated data that cannot be properly > > + decoded. > > +* Reads in the middle of an encoded extent can be returned by setting > > + ``encoded_iov->unencoded_offset`` to non-zero. > > +* Truncated unencoded data (e.g., because the file does not end on a block > > + boundary) may be returned by setting ``encoded_iov->len`` to a value smaller > > + value than ``encoded_iov->unencoded_len - encoded_iov->unencoded_offset``. > > + > > +Writes > > +====== > > + > > +Encoded ``write_iter`` should (in addition to the usual accounting/checks done > > +by ``write_iter``): > > + > > +1. Call ``copy_encoded_iov_from_iter()`` to get and validate the > > + ``encoded_iov``. > > +2. Call ``generic_encoded_write_checks()`` instead of > > + ``generic_write_checks()``. > > +3. Check that the provided encoding in ``encoded_iov`` is supported. > > +4. Advance ``kiocb->ki_pos`` by ``encoded_iov->len``. > > +5. Return the size of the encoded data written. > > + > > +Again, there are a few details: > > + > > +* Encoded ``write_iter`` doesn't need to support writing unencoded data. > > +* ``write_iter`` should either write all of the encoded data or none of it; it > > + must not do partial writes. > > +* ``write_iter`` doesn't need to validate the encoded data; a subsequent read > > + may return, e.g., ``-EIO`` if the data is not valid. > > +* The user may lie about the unencoded size of the data; a subsequent read > > + should truncate or zero-extend the unencoded data rather than returning an > > + error. > > +* Be careful of page cache coherency. > > diff --git a/Documentation/filesystems/index.rst b/Documentation/filesystems/index.rst > > index 386eaad008b2..e074a3f1f856 100644 > > --- a/Documentation/filesystems/index.rst > > +++ b/Documentation/filesystems/index.rst > > @@ -37,6 +37,7 @@ filesystem implementations. > > journalling > > fscrypt > > fsverity > > + encoded_io > > > > Filesystems > > =========== > > diff --git a/include/linux/fs.h b/include/linux/fs.h > > index 3cd4fe6b845e..aa7efd3430d1 100644 > > --- a/include/linux/fs.h > > +++ b/include/linux/fs.h > > @@ -175,6 +175,9 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset, > > /* File does not contribute to nr_files count */ > > #define FMODE_NOACCOUNT ((__force fmode_t)0x20000000) > > > > +/* File supports encoded IO */ > > +#define FMODE_ENCODED_IO ((__force fmode_t)0x40000000) > > + > > /* > > * Flag for rw_copy_check_uvector and compat_rw_copy_check_uvector > > * that indicates that they should check the contents of the iovec are > > @@ -314,6 +317,7 @@ enum rw_hint { > > #define IOCB_SYNC (1 << 5) > > #define IOCB_WRITE (1 << 6) > > #define IOCB_NOWAIT (1 << 7) > > +#define IOCB_ENCODED (1 << 8) > > > > struct kiocb { > > struct file *ki_filp; > > @@ -3109,6 +3113,13 @@ extern int sb_min_blocksize(struct super_block *, int); > > extern int generic_file_mmap(struct file *, struct vm_area_struct *); > > extern int generic_file_readonly_mmap(struct file *, struct vm_area_struct *); > > extern ssize_t generic_write_checks(struct kiocb *, struct iov_iter *); > > +struct encoded_iov; > > +extern int generic_encoded_write_checks(struct kiocb *, > > + const struct encoded_iov *); > > +extern int copy_encoded_iov_from_iter(struct encoded_iov *, struct iov_iter *); > > +extern ssize_t generic_encoded_read_checks(struct kiocb *, struct iov_iter *); > > +extern int copy_encoded_iov_to_iter(const struct encoded_iov *, > > + struct iov_iter *); > > extern int generic_remap_checks(struct file *file_in, loff_t pos_in, > > struct file *file_out, loff_t pos_out, > > loff_t *count, unsigned int remap_flags); > > @@ -3434,6 +3445,11 @@ static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags) > > return -EOPNOTSUPP; > > ki->ki_flags |= IOCB_NOWAIT; > > } > > + if (flags & RWF_ENCODED) { > > + if (!(ki->ki_filp->f_mode & FMODE_ENCODED_IO)) > > + return -EOPNOTSUPP; > > + ki->ki_flags |= IOCB_ENCODED; > > + } > > if (flags & RWF_HIPRI) > > ki->ki_flags |= IOCB_HIPRI; > > if (flags & RWF_DSYNC) > > diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h > > index 379a612f8f1d..f8c6c1e08def 100644 > > --- a/include/uapi/linux/fs.h > > +++ b/include/uapi/linux/fs.h > > @@ -278,6 +278,34 @@ struct fsxattr { > > SYNC_FILE_RANGE_WAIT_BEFORE | \ > > SYNC_FILE_RANGE_WAIT_AFTER) > > > > +enum { > > + ENCODED_IOV_COMPRESSION_NONE, > > +#define ENCODED_IOV_COMPRESSION_NONE ENCODED_IOV_COMPRESSION_NONE > > + ENCODED_IOV_COMPRESSION_ZLIB, > > +#define ENCODED_IOV_COMPRESSION_ZLIB ENCODED_IOV_COMPRESSION_ZLIB > > + ENCODED_IOV_COMPRESSION_LZO, > > +#define ENCODED_IOV_COMPRESSION_LZO ENCODED_IOV_COMPRESSION_LZO > > + ENCODED_IOV_COMPRESSION_ZSTD, > > +#define ENCODED_IOV_COMPRESSION_ZSTD ENCODED_IOV_COMPRESSION_ZSTD > > + ENCODED_IOV_COMPRESSION_TYPES = ENCODED_IOV_COMPRESSION_ZSTD, > > +}; > > + > > +enum { > > + ENCODED_IOV_ENCRYPTION_NONE, > > +#define ENCODED_IOV_ENCRYPTION_NONE ENCODED_IOV_ENCRYPTION_NONE > > + ENCODED_IOV_ENCRYPTION_TYPES = ENCODED_IOV_ENCRYPTION_NONE, > > +}; > > + > > What are those defines??? They're so you can check whether an enum value is defined in the UAPI headers via ifdef. E.g., if we were to add ENCODED_IOV_COMPRESSION_SOME_NEW_ALGORITHM, applications could use: #ifndef ENCODED_IOV_COMPRESSION_SOME_NEW_ALGORITHM #define ENCODED_IOV_COMPRESSION_SOME_NEW_ALGORITHM 4 #endif In my experience, this makes dealing with lagging UAPI headers less annoying. This is done elsewhere in UAPI headers (e.g., include/uapi/linux/in.h).