btrfs-progs: check/lowmem mode: Check inline extent size

[platform/upstream/btrfs-progs.git] / Documentation / btrfs-send.asciidoc

diff --git a/Documentation/btrfs-send.asciidoc b/Documentation/btrfs-send.asciidoc
index 6721428..cd7ada7 100644 (file)
--- a/Documentation/btrfs-send.asciidoc
+++ b/Documentation/btrfs-send.asciidoc
@@ -3,7 +3,7 @@ btrfs-send(8)
 
 NAME
 ----
-btrfs-send - send data of subvolume(s) to stdout/file.
+btrfs-send - generate a stream of changes between two subvolume snapshots
 
 SYNOPSIS
 --------
@@ -11,35 +11,56 @@ SYNOPSIS
 
 DESCRIPTION
 -----------
-Sends the subvolume(s) specified by <subvol> to stdout.
 
-By default, this will send the whole subvolume. To do an incremental
-send, use '-p <parent>'.
+This command will generate a stream of instructions that describe changes
+between two subvolume snapshots. The stream can be consumed by the *btrfs
+receive* command to replicate the sent snapshot on a different filesystem.
+The command operates in two modes: full and incremental.
 
-If you want to allow btrfs to clone from any additional local snapshots,
-use '-c <clone-src>' (multiple times where applicable). 
+All snapshots involved in one send command must be read-only, and this status
+cannot be changed as long as there's a running send operation that uses the
+snapshot.
 
-You must not specify clone sources unless you guarantee that these snapshots
-are exactly in the same state on both sides, the sender and the receiver.
+In the full mode, the entire snapshot data and metadata will end up in the
+stream.
+
+In the incremental mode (options '-p' and '-c'), previously sent snapshots that
+are available on both the sending and receiving side can be used to reduce the
+amount of information that has to be sent to reconstruct the sent snapshot on a
+different filesystem.
 
-It is allowed to omit the '-p <parent>' option when '-c <clone-src>' options
-are given, in which case *btrfs send* will determine a suitable parent among the
-clone sources itself.
+The '-p <parent>' option can be omitted when '-c <clone-src>' options are
+given, in which case *btrfs send* will determine a suitable parent from among
+the clone sources.
+
+You must not specify clone sources unless you guarantee that these snapshots
+are exactly in the same state on both sides--both for the sender and the
+receiver.
 
 `Options`
 
--v::
-Enable verbose debug output. Each occurrence of this option increases the
-verbose level more.
 -e::
-If sending multiple subvols at once, use the new format and omit the <end cmd> between the subvols.
+if sending multiple subvolumes at once, use the new format and omit the
+'end cmd' marker in the stream separating the subvolumes
 -p <parent>::
-Send an incremental stream from <parent> to <subvol>.
+send an incremental stream from 'parent' to 'subvol'
 -c <clone-src>::
-Use this snapshot as a clone source for an incremental send (multiple allowed).
+use this snapshot as a clone source for an incremental send (multiple allowed)
 -f <outfile>::
-Output is normally written to stdout. To write to a file, use this option.
-An alternative would be to use pipes.
+output is normally written to standard output so it can be, for example, piped
+to btrfs receive. Use this option to write it to a file instead.
+--no-data::
+send in 'NO_FILE_DATA' mode
++
+The output stream does not contain any file
+data and thus cannot be used to transfer changes. This mode is faster and
+is useful to show the differences in metadata.
+
+-v|--verbose::
+enable verbose output, print generated commands in a readable form, (each
+occurrence of this option increases the verbosity level)
+-q|--quiet::
+suppress all messages except errors
 
 EXIT STATUS
 -----------