From: Himanshu Madhani <himanshu.madhani@xxxxxxxxxx> Add RWF_ATOMIC flag description for pwritev2(). Signed-off-by: Himanshu Madhani <himanshu.madhani@xxxxxxxxxx> [jpg: complete rewrite] Signed-off-by: John Garry <john.g.garry@xxxxxxxxxx> --- man/man2/readv.2 | 76 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 76 insertions(+) diff --git a/man/man2/readv.2 b/man/man2/readv.2 index eecde06dc..9c8a11324 100644 --- a/man/man2/readv.2 +++ b/man/man2/readv.2 @@ -193,6 +193,66 @@ which provides lower latency, but may use additional resources. .B O_DIRECT flag.) .TP +.BR RWF_ATOMIC " (since Linux 6.11)" +Requires that writes to regular files in block-based filesystems be issued with +torn-write protection. +Torn-write protection means that for a power 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. +This flag is meaningful only for +.BR pwritev2 (), +and its effect applies only to the data range written by the system call. +The total write length must be power-of-2 and must be sized in the range +.RI [ stx_atomic_write_unit_min , +.IR stx_atomic_write_unit_max ]. +The write must be at a naturally-aligned offset within the file with respect to +the total write length - +for example, +a write of length 32KB at a file offset of 32KB is permitted, +however a write of length 32KB at a file offset of 48KB is not permitted. +The upper limit of +.I iovcnt +for +.BR pwritev2 () +is in +.I stx_atomic_write_segments_max. +Torn-write protection only works with +.B O_DIRECT +flag, i.e. buffered writes are not supported. +To guarantee consistency from the write between a file's in-core state with the +storage device, +.BR fdatasync (2), +or +.BR fsync (2), +or +.BR open (2) +and either +.B O_SYNC +or +.B O_DSYNC, +or +.B pwritev2 () +and either +.B RWF_SYNC +or +.B RWF_DSYNC +is required. Flags +.B O_SYNC +or +.B RWF_SYNC +provide the strongest guarantees for +.BR RWF_ATOMIC, +in that all data and also file metadata updates will be persisted for a +successfully completed write. +Just using either flags +.B O_DSYNC +or +.B RWF_DSYNC +means that all data and any file updates will be persisted for a successfully +completed write. +Not using any sync flags means that there is no guarantee that data or +filesystem updates are persisted. +.TP .BR RWF_SYNC " (since Linux 4.7)" .\" commit e864f39569f4092c2b2bc72c773b6e486c7e3bd9 Provide a per-write equivalent of the @@ -279,10 +339,26 @@ values overflows an .I ssize_t value. .TP +.B EINVAL + For +.BR RWF_ATOMIC +set, +the combination of the sum of the +.I iov_len +values and the +.I offset +value does not comply with the length and offset torn-write protection rules. +.TP .B EINVAL The vector count, .IR iovcnt , is less than zero or greater than the permitted maximum. +For +.BR RWF_ATOMIC +set, this maximum is in +.I stx_atomic_write_segments_max +from +.I statx. .TP .B EOPNOTSUPP An unknown flag is specified in \fIflags\fP. -- 2.31.1
