On Wed, Jul 17, 2024 at 09:36:18AM +0000, John Garry wrote: > 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, Nit: these could be two sentences "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. Pickier nit: KiB, not KB. > +The upper limit of > +.I iovcnt > +for > +.BR pwritev2 () > +is in "is given by" ? > +.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 This sentence ^^ should start on a new line. > +.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. "any file updates" ? I /think/ the difference between O_SYNC and O_DSYNC is that O_DSYNC persists all data and file metadata updates for the file range that was written, whereas O_SYNC persists all data and file metadata updates for the entire file. Perhaps everything between "Flags O_SYNC or RWF_SYNC..." and "...for a successfully completed write." should instead refer readers to the notes about synchronized I/O flags in the openat manpage? > +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, "If RWF_ATOMIC is specified..." ? (to be a bit more consistent with the language around the AT_* flags in openat) > +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 (same) --D > +.I stx_atomic_write_segments_max > +from > +.I statx. > .TP > .B EOPNOTSUPP > An unknown flag is specified in \fIflags\fP. > -- > 2.31.1 >
