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. */ _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
