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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) To: John Garry , 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 , John Garry 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: List-Subscribe: List-Unsubscribe: John Garry writes: > From: Prasad Singamsetty > > 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 > #jpg: merge into single patch and much rewrite ^^^ this might be a miss I guess. > Signed-off-by: John Garry > --- > 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 > #include > #include > +#include > > #include > #include > @@ -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