From 0796e660859724f304155e094b6cf5739a610ae4 Mon Sep 17 00:00:00 2001 From: Theodore Ts'o Date: Tue, 12 Jun 2012 17:09:39 -0400 Subject: [PATCH] lsattr, chattr: add support for btrfs's No_COW flag Signed-off-by: "Theodore Ts'o" --- lib/e2p/pf.c | 1 + lib/ext2fs/ext2_fs.h | 1 + misc/chattr.1.in | 44 ++++++++++++++++++++++++++------------------ misc/chattr.c | 1 + 4 files changed, 29 insertions(+), 18 deletions(-) diff --git a/lib/e2p/pf.c b/lib/e2p/pf.c index f03193c..e2f8ce5 100644 --- a/lib/e2p/pf.c +++ b/lib/e2p/pf.c @@ -49,6 +49,7 @@ static struct flags_name flags_array[] = { { EXT2_TOPDIR_FL, "T", "Top_of_Directory_Hierarchies" }, { EXT4_EXTENTS_FL, "e", "Extents" }, { EXT4_HUGE_FILE_FL, "h", "Huge_file" }, + { FS_NOCOW_FL, "C", "No_COW" }, { 0, NULL, NULL } }; diff --git a/lib/ext2fs/ext2_fs.h b/lib/ext2fs/ext2_fs.h index f46a1a9..fb3f7cc 100644 --- a/lib/ext2fs/ext2_fs.h +++ b/lib/ext2fs/ext2_fs.h @@ -301,6 +301,7 @@ struct ext2_dx_countlimit { #define EXT4_EXTENTS_FL 0x00080000 /* Inode uses extents */ #define EXT4_EA_INODE_FL 0x00200000 /* Inode used for large EA */ /* EXT4_EOFBLOCKS_FL 0x00400000 was here */ +#define FS_NOCOW_FL 0x00800000 /* Do not cow file */ #define EXT4_SNAPFILE_FL 0x01000000 /* Inode is a snapshot */ #define EXT4_SNAPFILE_DELETED_FL 0x04000000 /* Snapshot is being deleted */ #define EXT4_SNAPFILE_SHRUNK_FL 0x08000000 /* Snapshot shrink has completed */ diff --git a/misc/chattr.1.in b/misc/chattr.1.in index 92f6d70..2500561 100644 --- a/misc/chattr.1.in +++ b/misc/chattr.1.in @@ -27,8 +27,8 @@ existing attributes of the files; `-' causes them to be removed; and .PP The letters `acdeijstuADST' select the new attributes for the files: append only (a), compressed (c), no dump (d), extent format (e), immutable (i), -data journalling (j), secure deletion (s), no tail-merging (t), -undeletable (u), no atime updates (A), synchronous directory updates (D), +data journalling (j), secure deletion (s), no tail-merging (t), +undeletable (u), no atime updates (A), synchronous directory updates (D), synchronous updates (S), and top of directory hierarchy (T). .PP The following attributes are read-only, and may be listed by @@ -55,15 +55,24 @@ not modified. This avoids a certain amount of disk I/O for laptop systems. .PP A file with the `a' attribute set can only be open in append mode for writing. -Only the superuser or a process possessing the CAP_LINUX_IMMUTABLE +Only the superuser or a process possessing the CAP_LINUX_IMMUTABLE capability can set or clear this attribute. .PP A file with the `c' attribute set is automatically compressed on the disk by the kernel. A read from this file returns uncompressed data. A write to -this file compresses data before storing them on the disk. Note: please +this file compresses data before storing them on the disk. Note: please make sure to read the bugs and limitations section at the end of this document. .PP +A file with the 'C' attribute set will not be subject to copy-on-write +updates. This flag is only supported on file systems which perform +copy-on-write. (Note: For btrfs, the 'C' flag should be +set on new or empty files. If it is set on a file which already has +data blocks, it is undefined when the blocks assigned to the file will +be fully stable. If the 'C' flag is set on a directory, it will have no +effect on the directory, but new files created in that directory will +the No_COW attribute.) +.PP When a directory with the `D' attribute set is modified, the changes are written synchronously on the disk; this is equivalent to the `dirsync' mount option applied to a subset of the files. @@ -72,9 +81,9 @@ A file with the `d' attribute set is not candidate for backup when the .BR dump (8) program is run. .PP -The 'E' attribute is used by the experimental compression patches to +The 'E' attribute is used by the experimental compression patches to indicate that a compressed file has a compression error. It may not be -set or reset using +set or reset using .BR chattr (1), although it can be displayed by .BR lsattr (1). @@ -84,7 +93,7 @@ the blocks on disk. It may not be removed using .BR chattr (1). .PP The 'I' attribute is used by the htree code to indicate that a directory -is being indexed using hashed trees. It may not be set or reset using +is being indexed using hashed trees. It may not be set or reset using .BR chattr (1), although it can be displayed by .BR lsattr (1). @@ -105,8 +114,8 @@ A file with the `j' attribute has all of its data written to the ext3 journal before being written to the file itself, if the filesystem is mounted with the "data=ordered" or "data=writeback" options. When the filesystem is mounted with the "data=journal" option all file data -is already journalled and this attribute has no effect. -Only the superuser or a process possessing the CAP_SYS_RESOURCE +is already journalled and this attribute has no effect. Only +the superuser or a process possessing the CAP_SYS_RESOURCE capability can set or clear this attribute. .PP When a file with the `s' attribute set is deleted, its blocks are zeroed @@ -117,7 +126,7 @@ When a file with the `S' attribute set is modified, the changes are written synchronously on the disk; this is equivalent to the `sync' mount option applied to a subset of the files. .PP -A directory with the 'T' attribute will be deemed to be the top of +A directory with the 'T' attribute will be deemed to be the top of directory hierarchies for the purposes of the Orlov block allocator. This is a hint to the block allocator used by ext3 and ext4 that the subdirectories under this directory are not related, and thus should be @@ -129,7 +138,7 @@ group subdirectories closer together where possible. .PP A file with the 't' attribute will not have a partial block fragment at the end of the file merged with other files (for those filesystems which -support tail-merging). This is necessary for applications such as LILO +support tail-merging). This is necessary for applications such as LILO which read the filesystem directly, and which don't understand tail-merged files. Note: As of this writing, the ext2 or ext3 filesystems do not (yet, except in very experimental patches) support tail-merging. @@ -139,15 +148,15 @@ saved. This allows the user to ask for its undeletion. Note: please make sure to read the bugs and limitations section at the end of this document. .PP -The 'X' attribute is used by the experimental compression patches to +The 'X' attribute is used by the experimental compression patches to indicate that a raw contents of a compressed file can be accessed -directly. It currently may not be set or reset using +directly. It currently may not be set or reset using .BR chattr (1), although it can be displayed by .BR lsattr (1). .PP -The 'Z' attribute is used by the experimental compression patches to -indicate a compressed file is dirty. It may not be set or reset using +The 'Z' attribute is used by the experimental compression patches to +indicate a compressed file is dirty. It may not be set or reset using .BR chattr (1), although it can be displayed by .BR lsattr (1). @@ -157,10 +166,9 @@ although it can be displayed by was written by Remy Card . It is currently being maintained by Theodore Ts'o . .SH BUGS AND LIMITATIONS -The `c', 's', and `u' attributes are not honored +The `c', 's', and `u' attributes are not honored by the ext2 and ext3 filesystems as implemented in the current mainline -Linux kernels. These attributes may be implemented -in future versions of the ext2 and ext3 filesystems. +Linux kernels. .PP The `j' option is only useful if the filesystem is mounted as ext3. .PP diff --git a/misc/chattr.c b/misc/chattr.c index 8a2d61f..141ea6e 100644 --- a/misc/chattr.c +++ b/misc/chattr.c @@ -107,6 +107,7 @@ static const struct flags_char flags_array[] = { { EXT2_UNRM_FL, 'u' }, { EXT2_NOTAIL_FL, 't' }, { EXT2_TOPDIR_FL, 'T' }, + { FS_NOCOW_FL, 'C' }, { 0, 0 } }; -- 1.8.3.1