From mboxrd@z Thu Jan 1 00:00:00 1970
Received: from mail-pl1-f172.google.com (mail-pl1-f172.google.com [209.85.214.172])
(using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits))
(No client certificate requested)
by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0D16C4C601;
Sat, 24 Feb 2024 18:16:29 +0000 (UTC)
Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.172
ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116;
t=1708798591; cv=none; b=l6SFnuNwAOxtQ7csihS1Mh+cd47lpaWA0T/mAcQ0wvc3Rz7i3q8Kcr1RzM4jC2axDmWA3BiDCZLhWoLPRkltDA31NnyofQGcDxECipK0cvUte+jq+N7/4YinK3Z9BDyu2uCUy9os50yQnxgr3yzgzuskVUqafZiA7kbsoA/+Yoc=
ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org;
s=arc-20240116; t=1708798591; c=relaxed/simple;
bh=dIfv8qMop+kGsMCDN0K2VzJu+N6ZIcYeM1OBQyb46MY=;
h=Date:Message-Id:From:To:Cc:Subject:In-Reply-To; b=JKIjsxdvwNKOxuINcYDzaduZwg88zdJNVZOzdenxvWgCox6dlWStqbxD2m5eAGHatneg/ZKM6JMHKkXRdysRKDTNatERiJZPfR383ia9t3ezkx8q6h6rFZJSHeSINiqFm+ke/bk6Z0wGykhjwajWHS2E22W/sxLjaH8HyXtiCwo=
ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=Yym7rF4+; arc=none smtp.client-ip=209.85.214.172
Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com
Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com
Authentication-Results: smtp.subspace.kernel.org;
dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Yym7rF4+"
Received: by mail-pl1-f172.google.com with SMTP id d9443c01a7336-1dbae7b8ff2so8168665ad.3;
Sat, 24 Feb 2024 10:16:29 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
d=gmail.com; s=20230601; t=1708798589; x=1709403389; darn=vger.kernel.org;
h=in-reply-to:subject:cc:to:from:message-id:date:from:to:cc:subject
:date:message-id:reply-to;
bh=wnu+Meyv/9BP7YNzzpJcTuolqRDU8rmnNUjfmWPj+9A=;
b=Yym7rF4+YBjHR0iPbmkebjrYBTQP30vPR50WyNBoZaCPKNFOTE9nakZBk8xG9PkeiD
H7xiHLMf4vbFH6kSJDpvkRvI3lhZhPMb8+c22i5/5fkrT7Z1X9+xLA0zRF5j4tXLYZit
c9qTZl53L58NgihS14XWGl8moFR6o7mAtwuTbdAX/lIi6UeeRm6PAuOuZHeopCUA8u24
DNEQdtJlDzsXtl7lZlzCWZrk2oukV/D/eoiHM7RKogqU1e5iBwZ32VFcIvheVJ+QPTx0
EICWm+gNtk10/PQq0NnrcCG/pbJkkNEk61otxxH9VrUWwXHe54+ali6Qi1lVXS+iPO4G
/BuQ==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
d=1e100.net; s=20230601; t=1708798589; x=1709403389;
h=in-reply-to:subject:cc:to:from:message-id:date:x-gm-message-state
:from:to:cc:subject:date:message-id:reply-to;
bh=wnu+Meyv/9BP7YNzzpJcTuolqRDU8rmnNUjfmWPj+9A=;
b=bLTLUTeOisPoZLVBPgPBAegwzs6qMZYZYSfJ2TD8LuW8/Ia9PPyPwI7lfxqXpTIHjM
h6fev7WrT/orUitWM9MJyiMjVEBsBVsCwSPSDtzwk64Q/BZv1zXzLzUdvPXBq63sorzp
WDLLEj76qjuhY768aSjKSuNyOVXxIF45nx8FtGrMeM+4m3En9KrVYp2b9mQJF3dESsqr
doXLfQ/bZad7udmEQRqWxKHlD9NWEZTK0/XH+ukhYUD29uVn5VK958CFbZ1yod2OyQ0V
xm6THLd8RBWx3cD/OnZGHK39bY4wbuBfOMsxdpLjmK1+IuU43JnwuQHvP+Hyi39T2MJH
H+Fw==
X-Forwarded-Encrypted: i=1; AJvYcCXCEIBtqglmI2TXr0YbKEGu5FdGk4/p5uPzl4KNi+hjf1Ob6KSIlQBUUmj0JyLmMdsKR8Z4ruq6LLKl5FX40GiUDbVrzuEaWeRakbuzs17i8qhssSYsCW2fKKIAWN5sBHKRLOgFs3i2n2Y8wuJr3En8BMZv+sOnOi/I1d/GwvkS8CAbkWePl5wL3mwchwTG9fCUABv/kzoWfokwMsPbDl7fBb2+1nIE23bl5wtM8k30t2p9aAFrSl3dU7riSfYO
X-Gm-Message-State: AOJu0YzNYvaehCgUf/+aM46pPwRY9GyFe8al8U1LyQwu3RdyX6KNIfw+
07ae+ttV/886T8LLTDyY7LYdRy2ufaczX8wFiY+v1q3peTFMSnKr
X-Google-Smtp-Source: AGHT+IEhIRn378wt+gFfTyZVVHdy0OnAOhjAUqJcKoAdAEpOzjhracPgpW4cwIY9SoPSruGG3Ym2nQ==
X-Received: by 2002:a17:902:d891:b0:1dc:6fec:15d8 with SMTP id b17-20020a170902d89100b001dc6fec15d8mr2875267plz.47.1708798589107;
Sat, 24 Feb 2024 10:16:29 -0800 (PST)
Received: from dw-tp ([171.76.80.106])
by smtp.gmail.com with ESMTPSA id ci7-20020a17090afc8700b0029996fd70e2sm1511031pjb.45.2024.02.24.10.16.21
(version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256);
Sat, 24 Feb 2024 10:16:28 -0800 (PST)
Date: Sat, 24 Feb 2024 23:46:19 +0530
Message-Id: <87v86d20ek.fsf@doe.com>
From: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
To: John Garry <john.g.garry@oracle.com>, axboe@kernel.dk, kbusch@kernel.org, hch@lst.de, sagi@grimberg.me, jejb@linux.ibm.com, martin.petersen@oracle.com, djwong@kernel.org, viro@zeniv.linux.org.uk, brauner@kernel.org, dchinner@redhat.com, jack@suse.cz
Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-fsdevel@vger.kernel.org, tytso@mit.edu, jbongio@google.com, linux-scsi@vger.kernel.org, ojaswin@linux.ibm.com, linux-aio@kvack.org, linux-btrfs@vger.kernel.org, io-uring@vger.kernel.org, nilay@linux.ibm.com, Prasad Singamsetty <prasad.singamsetty@oracle.com>, John Garry <john.g.garry@oracle.com>
Subject: Re: [PATCH v4 03/11] fs: Initial atomic write support
In-Reply-To: <20240219130109.341523-4-john.g.garry@oracle.com>
Precedence: bulk
X-Mailing-List: io-uring@vger.kernel.org
List-Id: <io-uring.vger.kernel.org>
List-Subscribe: <mailto:io-uring+subscribe@vger.kernel.org>
List-Unsubscribe: <mailto:io-uring+unsubscribe@vger.kernel.org>
John Garry <john.g.garry@oracle.com> writes:
> From: Prasad Singamsetty <prasad.singamsetty@oracle.com>
>
> An atomic write is a write issued with torn-write protection, meaning
> that for a power failure or any other hardware failure, all or none of the
> data from the write will be stored, but never a mix of old and new data.
>
> Userspace may add flag RWF_ATOMIC to pwritev2() to indicate that the
> write is to be issued with torn-write prevention, according to special
> alignment and length rules.
>
> For any syscall interface utilizing struct iocb, add IOCB_ATOMIC for
> iocb->ki_flags field to indicate the same.
>
> A call to statx will give the relevant atomic write info for a file:
> - atomic_write_unit_min
> - atomic_write_unit_max
> - atomic_write_segments_max
>
> Both min and max values must be a power-of-2.
>
> Applications can avail of atomic write feature by ensuring that the total
> length of a write is a power-of-2 in size and also sized between
> atomic_write_unit_min and atomic_write_unit_max, inclusive. Applications
> must ensure that the write is at a naturally-aligned offset in the file
> wrt the total write length. The value in atomic_write_segments_max
> indicates the upper limit for IOV_ITER iovcnt.
>
> Add file mode flag FMODE_CAN_ATOMIC_WRITE, so files which do not have the
> flag set will have RWF_ATOMIC rejected and not just ignored.
>
> Add a type argument to kiocb_set_rw_flags() to allows reads which have
> RWF_ATOMIC set to be rejected.
>
> Helper function atomic_write_valid() can be used by FSes to verify
> compliant writes.
>
> Signed-off-by: Prasad Singamsetty <prasad.singamsetty@oracle.com>
> #jpg: merge into single patch and much rewrite
^^^ this might be a miss I guess.
> Signed-off-by: John Garry <john.g.garry@oracle.com>
> ---
> fs/aio.c | 8 ++++----
> fs/btrfs/ioctl.c | 2 +-
> fs/read_write.c | 2 +-
> include/linux/fs.h | 36 +++++++++++++++++++++++++++++++++++-
> include/uapi/linux/fs.h | 5 ++++-
> io_uring/rw.c | 4 ++--
> 6 files changed, 47 insertions(+), 10 deletions(-)
>
> diff --git a/fs/aio.c b/fs/aio.c
> index bb2ff48991f3..21bcbc076fd0 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -1502,7 +1502,7 @@ static void aio_complete_rw(struct kiocb *kiocb, long res)
> iocb_put(iocb);
> }
>
> -static int aio_prep_rw(struct kiocb *req, const struct iocb *iocb)
> +static int aio_prep_rw(struct kiocb *req, const struct iocb *iocb, int type)
maybe rw_type?
> {
> int ret;
>
> @@ -1528,7 +1528,7 @@ static int aio_prep_rw(struct kiocb *req, const struct iocb *iocb)
> } else
> req->ki_ioprio = get_current_ioprio();
>
> - ret = kiocb_set_rw_flags(req, iocb->aio_rw_flags);
> + ret = kiocb_set_rw_flags(req, iocb->aio_rw_flags, type);
> if (unlikely(ret))
> return ret;
>
> @@ -1580,7 +1580,7 @@ static int aio_read(struct kiocb *req, const struct iocb *iocb,
> struct file *file;
> int ret;
>
> - ret = aio_prep_rw(req, iocb);
> + ret = aio_prep_rw(req, iocb, READ);
> if (ret)
> return ret;
> file = req->ki_filp;
> @@ -1607,7 +1607,7 @@ static int aio_write(struct kiocb *req, const struct iocb *iocb,
> struct file *file;
> int ret;
>
> - ret = aio_prep_rw(req, iocb);
> + ret = aio_prep_rw(req, iocb, WRITE);
> if (ret)
> return ret;
> file = req->ki_filp;
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index ac3316e0d11c..455f06d94b11 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -4555,7 +4555,7 @@ static int btrfs_ioctl_encoded_write(struct file *file, void __user *argp, bool
> goto out_iov;
>
> init_sync_kiocb(&kiocb, file);
> - ret = kiocb_set_rw_flags(&kiocb, 0);
> + ret = kiocb_set_rw_flags(&kiocb, 0, WRITE);
> if (ret)
> goto out_iov;
> kiocb.ki_pos = pos;
> diff --git a/fs/read_write.c b/fs/read_write.c
> index d4c036e82b6c..a7dc1819192d 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -730,7 +730,7 @@ static ssize_t do_iter_readv_writev(struct file *filp, struct iov_iter *iter,
> ssize_t ret;
>
> init_sync_kiocb(&kiocb, filp);
> - ret = kiocb_set_rw_flags(&kiocb, flags);
> + ret = kiocb_set_rw_flags(&kiocb, flags, type);
> if (ret)
> return ret;
> kiocb.ki_pos = (ppos ? *ppos : 0);
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 023f37c60709..7271640fd600 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -43,6 +43,7 @@
> #include <linux/cred.h>
> #include <linux/mnt_idmapping.h>
> #include <linux/slab.h>
> +#include <linux/uio.h>
>
> #include <asm/byteorder.h>
> #include <uapi/linux/fs.h>
> @@ -119,6 +120,10 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
> #define FMODE_PWRITE ((__force fmode_t)0x10)
> /* File is opened for execution with sys_execve / sys_uselib */
> #define FMODE_EXEC ((__force fmode_t)0x20)
> +
> +/* File supports atomic writes */
> +#define FMODE_CAN_ATOMIC_WRITE ((__force fmode_t)0x40)
> +
> /* 32bit hashes as llseek() offset (for directories) */
> #define FMODE_32BITHASH ((__force fmode_t)0x200)
> /* 64bit hashes as llseek() offset (for directories) */
> @@ -328,6 +333,7 @@ enum rw_hint {
> #define IOCB_SYNC (__force int) RWF_SYNC
> #define IOCB_NOWAIT (__force int) RWF_NOWAIT
> #define IOCB_APPEND (__force int) RWF_APPEND
> +#define IOCB_ATOMIC (__force int) RWF_ATOMIC
>
You might also want to add this definition in here too
#define TRACE_IOCB_STRINGS \
<...>
<...>
{ IOCB_ATOMIC, "ATOMIC" }
> /* non-RWF related bits - start at 16 */
> #define IOCB_EVENTFD (1 << 16)
> @@ -3321,7 +3327,7 @@ static inline int iocb_flags(struct file *file)
> return res;
> }
>
> -static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
> +static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags, int type)
maybe rw_type?
> {
> int kiocb_flags = 0;
>
> @@ -3338,6 +3344,12 @@ static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
> return -EOPNOTSUPP;
> kiocb_flags |= IOCB_NOIO;
> }
> + if (flags & RWF_ATOMIC) {
> + if (type == READ)
> + return -EOPNOTSUPP;
> + if (!(ki->ki_filp->f_mode & FMODE_CAN_ATOMIC_WRITE))
> + return -EOPNOTSUPP;
> + }
> kiocb_flags |= (__force int) (flags & RWF_SUPPORTED);
> if (flags & RWF_SYNC)
> kiocb_flags |= IOCB_DSYNC;
> @@ -3523,4 +3535,26 @@ extern int vfs_fadvise(struct file *file, loff_t offset, loff_t len,
> extern int generic_fadvise(struct file *file, loff_t offset, loff_t len,
> int advice);
>
> +static inline bool atomic_write_valid(loff_t pos, struct iov_iter *iter,
> + unsigned int unit_min, unsigned int unit_max)
> +{
> + size_t len = iov_iter_count(iter);
> +
> + if (!iter_is_ubuf(iter))
> + return false;
There is no mention about this limitation in the commit message of this
patch. Maybe it will be good to capture why this limitation to only
support ubuf and/or any plans to lift this restriction in future
in the commit message?
> +
> + if (len == unit_min || len == unit_max) {
> + /* ok if exactly min or max */
> + } else if (len < unit_min || len > unit_max) {
> + return false;
> + } else if (!is_power_of_2(len)) {
> + return false;
> + }
Checking for len == unit_min || len == unit_max is redundant when
unit_min and unit_max are already power of 2.
> +
> + if (pos & (len - 1))
> + return false;
> +
> + return true;
> +}
> +
> #endif /* _LINUX_FS_H */
> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index 48ad69f7722e..a0975ae81e64 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -301,9 +301,12 @@ typedef int __bitwise __kernel_rwf_t;
> /* per-IO O_APPEND */
> #define RWF_APPEND ((__force __kernel_rwf_t)0x00000010)
>
> +/* Atomic Write */
> +#define RWF_ATOMIC ((__force __kernel_rwf_t)0x00000040)
> +
> /* mask of flags supported by the kernel */
> #define RWF_SUPPORTED (RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT |\
> - RWF_APPEND)
> + RWF_APPEND | RWF_ATOMIC)
>
> /* Pagemap ioctl */
> #define PAGEMAP_SCAN _IOWR('f', 16, struct pm_scan_arg)
> diff --git a/io_uring/rw.c b/io_uring/rw.c
> index d5e79d9bdc71..f8c022301cf4 100644
> --- a/io_uring/rw.c
> +++ b/io_uring/rw.c
> @@ -719,7 +719,7 @@ static int io_rw_init_file(struct io_kiocb *req, fmode_t mode)
> struct kiocb *kiocb = &rw->kiocb;
> struct io_ring_ctx *ctx = req->ctx;
> struct file *file = req->file;
> - int ret;
> + int ret, type = (mode == FMODE_WRITE) ? WRITE : READ;
>
> if (unlikely(!file || !(file->f_mode & mode)))
> return -EBADF;
> @@ -728,7 +728,7 @@ static int io_rw_init_file(struct io_kiocb *req, fmode_t mode)
> req->flags |= io_file_get_flags(file);
>
> kiocb->ki_flags = file->f_iocb_flags;
> - ret = kiocb_set_rw_flags(kiocb, rw->flags);
> + ret = kiocb_set_rw_flags(kiocb, rw->flags, type);
> if (unlikely(ret))
> return ret;
> kiocb->ki_flags |= IOCB_ALLOC_CACHE;
> --
> 2.31.1