Date: Sun, 6 Dec 2020 20:50:22 +0000 (UTC) From: Kirk McKusick <mckusick@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r368396 - in head/sys: fs/ext2fs ufs/ufs Message-ID: <202012062050.0B6KoMcE057354@repo.freebsd.org>
next in thread | raw e-mail | index | archive | help
Author: mckusick Date: Sun Dec 6 20:50:21 2020 New Revision: 368396 URL: https://svnweb.freebsd.org/changeset/base/368396 Log: Document the BA_CLRBUF flag used in ufs and ext2fs filesystems. Suggested by: kib MFC after: 3 days Sponsored by: Netflix Modified: head/sys/fs/ext2fs/ext2_extern.h head/sys/ufs/ufs/ufs_extern.h Modified: head/sys/fs/ext2fs/ext2_extern.h ============================================================================== --- head/sys/fs/ext2fs/ext2_extern.h Sun Dec 6 19:24:38 2020 (r368395) +++ head/sys/fs/ext2fs/ext2_extern.h Sun Dec 6 20:50:21 2020 (r368396) @@ -135,6 +135,13 @@ void ext2_gd_csum_set(struct m_ext2fs *); /* Flags to low-level allocation routines. * The low 16-bits are reserved for IO_ flags from vnode.h. + * + * The BA_CLRBUF flag specifies that the existing content of the block + * will not be completely overwritten by the caller, so buffers for new + * blocks must be cleared and buffers for existing blocks must be read. + * When BA_CLRBUF is not set the buffer will be completely overwritten + * and there is no reason to clear them or to spend I/O fetching existing + * data. The BA_CLRBUF flag is handled in the UFS_BALLOC() functions. */ #define BA_CLRBUF 0x00010000 /* Clear invalid areas of buffer. */ #define BA_SEQMASK 0x7F000000 /* Bits holding seq heuristic. */ Modified: head/sys/ufs/ufs/ufs_extern.h ============================================================================== --- head/sys/ufs/ufs/ufs_extern.h Sun Dec 6 19:24:38 2020 (r368395) +++ head/sys/ufs/ufs/ufs_extern.h Sun Dec 6 20:50:21 2020 (r368396) @@ -119,6 +119,13 @@ void softdep_revert_rmdir(struct inode *, struct inode * * Note: The general vfs code typically limits the sequential heuristic * count to 127. See sequential_heuristic() in kern/vfs_vnops.c + * + * The BA_CLRBUF flag specifies that the existing content of the block + * will not be completely overwritten by the caller, so buffers for new + * blocks must be cleared and buffers for existing blocks must be read. + * When BA_CLRBUF is not set the buffer will be completely overwritten + * and there is no reason to clear them or to spend I/O fetching existing + * data. The BA_CLRBUF flag is handled in the UFS_BALLOC() functions. */ #define BA_CLRBUF 0x00010000 /* Clear invalid areas of buffer. */ #define BA_METAONLY 0x00020000 /* Return indirect block buffer. */
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?202012062050.0B6KoMcE057354>