mirror of
https://github.com/freebsd/freebsd-src.git
synced 2026-10-28 11:25:21 +01:00
Maxim Sobolev
26d84bb8bf
For a synchronous write, ffs_write() writes the data buffers with bwrite() and then the inode with ffs_update(vp, 1). With soft updates, a new block pointer can only reach the disk after the dependencies of the block, such as the cylinder group map that allocates it, are written. Until then initiate_write_inodeblock_ufs[12]() and initiate_write_indirdep() roll the pointer, and for an extending write the size, back in the buffer being written. Nothing in the write path flushes those dependencies, so the inode went out with the old size and pointers, ffs_update() cleared IN_SIZEMOD and IN_IBLKDATA, and a crash before the syncer rewrote the inode lost data that O_SYNC or O_DSYNC promised was on stable storage. The same held for a new block below an indirect block, which ffs_balloc() writes synchronously but with the pointer rolled back. When soft updates are enabled and the write allocated blocks, finish it with ffs_syncvnode(), as fsync(2) and fdatasync(2) do: it flushes the dependencies, rewrites the rolled back indirect blocks and writes the inode, or for O_DSYNC only writes the inode when IN_SIZEMOD or IN_IBLKDATA say it is needed. The flags cannot tell whether the write allocated anything, because allocating a block below an existing indirect block sets neither, so compare the inode's block count before and after the write instead. A write that allocated nothing, such as an overwrite of existing blocks, adds no dependencies of its own and keeps writing only the inode, so that it does not pay for a sync of the whole vnode. ffs_syncvnode() only drops the vnode lock when it has to resolve directory dependencies, which ffs_write() never sees. ffs_syncvnode() also writes whatever other descriptors left dirty on the vnode, so the first synchronous write after a lot of buffered writes would pay for all of them. To put that cost on the open instead, where it is less unexpected for a descriptor opened for synchronous writes, add ffs_open() and, with soft updates, sync the vnode there when a regular file is opened for writing with O_SYNC or O_DSYNC, the same way the writes would: a full sync for O_SYNC, a data-only one for O_DSYNC. It calls ffs_syncvnode() rather than VOP_FSYNC(), whose softdep_fsync() may drop the vnode lock in the middle of the open. The sync on open only moves work that the writes would otherwise do, so it is skipped rather than waited for when writes are suspended, and its errors do not fail the open. Without soft updates the writes sync nothing but their own blocks and the inode, so there is nothing to move and the open does not sync. Sponsored by: Sippy Software, Inc. Reviewed by: kib Tested by: pho Differential Revision: https://reviews.freebsd.org/D60134 MFC after: 1 month
FreeBSD Source:
This is the top level of the FreeBSD source directory.
FreeBSD is an operating system used to power modern servers, desktops, and embedded platforms. A large community has continually developed it for more than thirty years. Its advanced networking, security, and storage features have made FreeBSD the platform of choice for many of the busiest web sites and most pervasive embedded networking and storage devices.
For copyright information, please see the file COPYRIGHT in this directory. Additional copyright information also exists for some sources in this tree - please see the specific source directories for more information.
The Makefile in this directory supports a number of targets for building components (or all) of the FreeBSD source tree. See build(7), config(8), FreeBSD handbook on building userland, and Handbook for kernels for more information, including setting make(1) variables.
For information on the CPU architectures and platforms supported by FreeBSD, see the FreeBSD website's Platforms page.
For official FreeBSD bootable images, see the release page.
Source Roadmap:
| Directory | Description |
|---|---|
| bin | System/user commands. |
| cddl | Source code for third-party software under the Common Development and Distribution License. |
| contrib | Source code for third-party software. |
| crypto | Source code for cryptographic libraries and commands (see crypto/README). |
| etc | Template files for /etc. |
| include | System include files. |
| kerberos5 | Build system for Kerberos 5 (Heimdal). |
| krb5 | Build system for Kerberos 5 (MIT). |
| lib | System libraries. |
| libexec | System commands intended to be executed by other commands or daemons. |
| packages | Base system packages. |
| release | Makefiles and scripts used for building releases and VM images. |
| rescue | Build system for statically linked /rescue commands. |
| sbin | System commands. |
| secure | Build system for cryptographic libraries and commands (excluding Kerberos). |
| share | Shared resources. |
| stand | Boot loader sources. |
| sys | Kernel sources (see sys/README.md). |
| targets | Support for experimental DIRDEPS_BUILD |
| tests | Tests which can be run by Kyua. See tests/README for additional information. |
| tools | Ancillary utilities and tests (not included in the build). |
| usr.bin | User commands. |
| usr.sbin | System administration commands. |
For information on synchronizing your source tree with one or more of the FreeBSD Project's development branches, please see FreeBSD Handbook.