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 | 61 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 61 insertions(+) diff --git a/man/man2/readv.2 b/man/man2/readv.2 index eecde06dc..7737eb65c 100644 --- a/man/man2/readv.2 +++ b/man/man2/readv.2 @@ -237,6 +237,50 @@ the data is always appended to the end of the file. However, if the .I offset argument is \-1, the current file offset is updated. +.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 32KiB at a file offset of 32KiB is permitted, +however a write of length 32KiB at a file offset of 48KiB is not permitted. +The upper limit of +.I iovcnt +for +.BR pwritev2 () +is given by the value 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, +.B O_SYNC +or +.B O_DSYNC +must be specified for +.BR open (2). +The same synchronized I/O guarantees as described in +.BR open (2) +are provided when these flags or their equivalent flags and system calls are +used (e.g. +if +.BR RWF_SYNC +is specified for +.BR pwritev2 () +). .SH RETURN VALUE On success, .BR readv (), @@ -280,9 +324,26 @@ values overflows an value. .TP .B EINVAL +If +.BR RWF_ATOMIC +is specified, +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. +If +.BR RWF_ATOMIC +is specified, +this maximum is given by the +.I stx_atomic_write_segments_max +value from +.I statx. .TP .B EOPNOTSUPP An unknown flag is specified in \fIflags\fP. -- 2.31.1
