Change Details

This is mostly the same as O_SYNC, but can potentially skip writing out stuff that isn't required for reading the data back. From the point of view of a file system, this is reported as the new flag IO_DATASYNC passed to VOP_WRITE(), along with the existing IO_SYNC flag. That means that filesystems that don't know about IO_DATASYNC yet can keep on doing what they're doing, but those that understand IO_DATASYNC can modify their behaviour. Once D25072 goes in, it should be possible to teach ffs_write() to understand IO_DATASYNC, to avoid unnecesssary inode write-back. Also, fix up some related outdated comments and man pages: a claim that f_flag is a short (not true for a very long time), some missing flags and a typo in fcntl.c, and some language that makes O_SYNC seem like second fiddle to O_FSYNC, when IMHO it should now be the other way around. Also, adjust the CDDL macro that redefines FDSYNC not to do that anymore. Even though with this patch it becomes a value distinct from FFSYNC, that's OK because zfs_vnops.c, zfs_log.c, zvol.c, vdev_file.c always test for (FSYNC | FDSYNC) anwyay. A separate patch will add O_DSYNC support for aio_fsync(2), see D25071.

This is mostly the same as O_SYNC, but can potentially skip writing out stuff that isn't required for reading the data back. From the point of view of a file system, this is reported as the new flag IO_DATASYNC passed to VOP_WRITE(), along with the existing IO_SYNC flag. That means that filesystems that don't know about IO_DATASYNC yet can keep on doing what they're doing, but those that understand IO_DATASYNC can modify their behaviour. Once D25072 goes in, it should be possible to teach ffs_write() to understand IO_DATASYNC, to avoid unnecesssary inode write-back. Also, fix up some related outdated comments and man pages: a claim that f_flag is a short (not true for a very long time), some missing flags and a typo in fcntl.c, and some language that makes O_SYNC seem like second fiddle to O_FSYNC, when IMHO it should now be the other way around. Also, adjust the ZFS macro that redefines FDSYNC not to do that anymore. Even though with this patch it becomes a value distinct from FFSYNC, that's OK because zfs_vnops.c, zfs_log.c, zvol.c, vdev_file.c always test for (FSYNC | FDSYNC) anwyay. A separate patch will add O_DSYNC support for aio_fsync(2), see D25071.

This is mostly the same as O_SYNC, but can potentially skip writing out stuff that isn't required for reading the data back. From the point of view of a file system, this is reported as the new flag IO_DATASYNC passed to VOP_WRITE(), along with the existing IO_SYNC flag. That means that filesystems that don't know about IO_DATASYNC yet can keep on doing what they're doing, but those that understand IO_DATASYNC can modify their behaviour. Once D25072 goes in, it should be possible to teach ffs_write() to understand IO_DATASYNC, to avoid unnecesssary inode write-back. Also, fix up some related outdated comments and man pages: a claim that f_flag is a short (not true for a very long time), some missing flags and a typo in fcntl.c, and some language that makes O_SYNC seem like second fiddle to O_FSYNC, when IMHO it should now be the other way around. Also, adjust the CDDLZFS macro that redefines FDSYNC not to do that anymore. Even though with this patch it becomes a value distinct from FFSYNC, that's OK because zfs_vnops.c, zfs_log.c, zvol.c, vdev_file.c always test for (FSYNC | FDSYNC) anwyay. A separate patch will add O_DSYNC support for aio_fsync(2), see D25071.