On Sat, Mar 23, 2013 at 12:48:54PM -0500, Eric Sandeen wrote:
> Document all current btrfs mount options.
>
> Signed-off-by: Eric Sandeen <sand...@redhat.com>
> ---
>
> please, Please, PLEASE review this and suggest improvements.
> I'm no btrfs wizard but I've done my best to get this all right
> based on commit logs, code reading, and wiki reading. In cases where
> any of those 3 disagreed, I've done my best to document reality, but I'm
> sure it could use corrections, clarifications, etc.
>
> In particular, some of these mount options could really use more
> description of why a user might want them, rather than simply stating
> what they do.
>
> "notreelog" is particularly egregious, as I have nothing but self-referential
> documentation.
>
> So this can use some iteration, I'm sure, but hopefully it's a decent
> start.
>
> Thanks,
> -Eric
>
> diff --git a/Documentation/filesystems/btrfs.txt
> b/Documentation/filesystems/btrfs.txt
> index 7671352..02a19c8 100644
> --- a/Documentation/filesystems/btrfs.txt
> +++ b/Documentation/filesystems/btrfs.txt
> @@ -1,6 +1,6 @@
>
> - BTRFS
> - =====
> +BTRFS
> +=====
>
> Btrfs is a new copy on write filesystem for Linux aimed at
> implementing advanced features while focusing on fault tolerance,
> @@ -34,9 +34,173 @@ The main Btrfs features include:
> * Online filesystem defragmentation
>
>
> -
> - MAILING LIST
> - ============
> +Mount Options
> +=============
> +
> +When mounting a btrfs filesystem, the following option are accepted.
> +Unless otherwise specified, all options default to off.
> +
> + alloc_start=<bytes>
> + Debugging option to force all block allocations above a threshold.
> + The value is specified in bytes, optionally with a K, M, or G suffix,
> + case insensitive. Default is 1MB.
> +
> + autodefrag
> + Detect small random writes into files and queue them up for the
> + defrag process. Works best for small files; Not well suited for
> + large database workloads.
> +
> + check_int
> + check_int_data
> + check_int_print_mask=<value>
> + These debugging options control the behavior of the integrity checking
> + module (the BTRFS_FS_CHECK_INTEGRITY config option required).
> +
> + check_int enables the integrity checker module, which examines all
> + block write requests to ensure on-disk consistency, at a large
> + memory and CPU cost.
> +
> + check_int_data includes extent data in the integrity checks, and
> + implies the check_int option.
> +
> + check_int_print_mask takes a bitmask of BTRFSIC_PRINT_MASK_* values
> + as defined in fs/btrfs/check-integrity.c, to control the integrity
> + checker module behavior.
> +
> + See comments at the top of fs/btrfs/check-integrity.c for more info.
> +
> + compress
> + compress=<type>
> + compress-force
> + compress-force=<type>
> + Control BTRFS file data compression. Type may be specified as "zlib"
> + "lzo" or "no" (for no compression, used for remounting). If no type
> + is specified, zlib is used. If compress-force is specified,
> + all files will be compressed, whether or not they compress well.
> + If compression is enabled, nodatacow and nodatasum are disabled.
> +
> + degraded
> + Allow mounts to continue with missing devices. A read-write mount may
> + fail with too many devices missing, for example if a stripe member
> + is completely missing.
> +
> + device=<devicepath>
> + Specify a device during mount so that ioctls on the control device
> + can be avoided. Especialy useful when trying to mount a multi-device
> + setup as root. May be specified multiple times for multiple devices.
> +
> + discard
> + Issue command to let the block device reclaim space freed by the
> + filesystem. This is useful for SSD devices, thinly provisioned
> + LUNs and virtual machine images, but may have a performance
> + impact.
> +
> + enospc_debug
> + Debugging option to be more verbose in some ENOSPC conditions.
> +
> + fatal_errors=<action>
> + Action to take when encountering a fatal error:
> + "bug" - BUG() on a fatal error. This is the default.
> + "panic" - panic() on a fatal error.
> +
> + flushoncommit
> + The 'flushoncommit' mount option forces any data dirtied by a write in a
> + prior transaction to commit as part of the current commit. This makes
> + the committed state a fully consistent view of the file system from the
> + application's perspective (i.e., it includes all completed file system
> + operations). This was previously the behavior only when a snapshot is
> + created.
> +
> + inode_cache
> + Enable free inode number caching. Defaults to off due to an overflow
> + problem when the free space crcs don't fit inside a single page.
> +
> + max_inline=<bytes>
> + Specify the maximum amount of space, in bytes, that can be inlined in
> + a metadata B-tree leaf. The value is specified in bytes, optionally
> + with a K, M, or G suffix, case insensitive. In practice, this value
> + is limited by the root sector size, with some space unavailable due
> + to leaf headers. For a 4k sectorsize, max inline data is ~3900 bytes.
> +
> + metadata_ratio=<value>
> + Specify that 1 metadata chunk should be allocated after every <value>
> + data chunks. Off by default.
> +
> + noacl
> + Disable support for Posix Access Control Lists (ACLs). See the
> + acl(5) manual page for more information about ACLs.
> +
> + nobarrier
> + Disables the use of block layer write barriers. Write barriers
> ensure
> + that certain IOs make it through the device cache and are on persistent
> + storage. If used on a device with a volatile (non-battery-backed)
> + write-back cache, this option will lead to filesystem corruption on a
> + system crash or power loss.
> +
> + nodatacow
> + Disable data copy-on-write for newly created files. Implies nodatasum,
> + and disables all compression.
> +
> + nodatasum
> + Disable data checksumming for newly created files.
> +
> + notreelog
> + Disable the tree logging used for fsync and O_SYNC writes.
> +
> + recovery
> + Enable autorecovery attempts if a bad tree root is found at mount time.
> + Currently this scans a list of several previous tree roots and tries to
> + use the first readable.
> +
> + skip_balance
> + Skip automatic restart of previous balance operation after mount. May
resume interrupted
> + be restarted with "btrfs device balance"
May be resumed with "btrfs balance resume" or cancelled with "btrfs
balance cancel". skip_balance simply keeps balance in paused state.
Feel free to word this appropriately ;)
Thanks,
Ilya
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