Merge remote-tracking branch 'remotes/lalrae/tags/mips-20141107' into staging

[qemu.git] / qemu-doc.texi

diff --git a/qemu-doc.texi b/qemu-doc.texi
index 6d684e2c212b0b7a214b4da3442482cc70ceb82c..9973090c6cb9a1968159ee4291eea840a53c2fec 100644 (file)
--- a/qemu-doc.texi
+++ b/qemu-doc.texi
@@ -527,6 +527,15 @@ Linux or NTFS on Windows), then only the written sectors will reserve
 space. Use @code{qemu-img info} to know the real size used by the
 image or @code{ls -ls} on Unix/Linux.
 
+Supported options:
+@table @code
+@item preallocation
+Preallocation mode (allowed values: @code{off}, @code{falloc}, @code{full}).
+@code{falloc} mode preallocates space for image by calling posix_fallocate().
+@code{full} mode preallocates space for image by writing zeros to underlying
+storage.
+@end table
+
 @item qcow2
 QEMU image format, the most versatile format. Use it to have smaller
 images (useful if your filesystem does not supports holes, for example
@@ -575,9 +584,11 @@ sizes can improve the image file size whereas larger cluster sizes generally
 provide better performance.
 
 @item preallocation
-Preallocation mode (allowed values: off, metadata). An image with preallocated
-metadata is initially larger but can improve performance when the image needs
-to grow.
+Preallocation mode (allowed values: @code{off}, @code{metadata}, @code{falloc},
+@code{full}). An image with preallocated metadata is initially larger but can
+improve performance when the image needs to grow. @code{falloc} and @code{full}
+preallocations are like the same options of @code{raw} format, but sets up
+metadata also.
 
 @item lazy_refcounts
 If this option is set to @code{on}, reference count updates are postponed with
@@ -589,6 +600,22 @@ check -r all} is required, which may take some time.
 
 This option can only be enabled if @code{compat=1.1} is specified.
 
+@item nocow
+If this option is set to @code{on}, it will turn off COW of the file. It's only
+valid on btrfs, no effect on other file systems.
+
+Btrfs has low performance when hosting a VM image file, even more when the guest
+on the VM also using btrfs as file system. Turning off COW is a way to mitigate
+this bad performance. Generally there are two ways to turn off COW on btrfs:
+a) Disable it by mounting with nodatacow, then all newly created files will be
+NOCOW. b) For an empty file, add the NOCOW file attribute. That's what this option
+does.
+
+Note: this option is only valid to new or empty files. If there is an existing
+file which is COW and has data blocks already, it couldn't be changed to NOCOW
+by setting @code{nocow=on}. One can issue @code{lsattr filename} to check if
+the NOCOW flag is set or not (Capital 'C' is NOCOW flag).
+
 @end table
 
 @item qed
@@ -627,15 +654,6 @@ File name of a base image (see @option{create} subcommand)
 If this option is set to @code{on}, the image is encrypted.
 @end table
 
-@item cow
-User Mode Linux Copy On Write image format. It is supported only for
-compatibility with previous versions.
-Supported options:
-@table @code
-@item backing_file
-File name of a base image (see @option{create} subcommand)
-@end table
-
 @item vdi
 VirtualBox 1.1 compatible image format.
 Supported options:
@@ -823,7 +841,7 @@ In this case, the block device must be exported using qemu-nbd:
 qemu-nbd --socket=/tmp/my_socket my_disk.qcow2
 @end example
 
-The use of qemu-nbd allows to share a disk between several guests:
+The use of qemu-nbd allows sharing of a disk between several guests:
 @example
 qemu-nbd --socket=/tmp/my_socket --share=2 my_disk.qcow2
 @end example
@@ -1189,9 +1207,16 @@ In order to check that the user mode network is working, you can ping
 the address 10.0.2.2 and verify that you got an address in the range
 10.0.2.x from the QEMU virtual DHCP server.
 
-Note that @code{ping} is not supported reliably to the internet as it
-would require root privileges. It means you can only ping the local
-router (10.0.2.2).
+Note that ICMP traffic in general does not work with user mode networking.
+@code{ping}, aka. ICMP echo, to the local router (10.0.2.2) shall work,
+however. If you're using QEMU on Linux >= 3.0, it can use unprivileged ICMP
+ping sockets to allow @code{ping} to the Internet. The host admin has to set
+the ping_group_range in order to grant access to those sockets. To allow ping
+for GID 100 (usually users group):
+
+@example
+echo 100 100 > /proc/sys/net/ipv4/ping_group_range
+@end example
 
 When using the built-in TFTP server, the router is also the TFTP
 server.
@@ -1938,7 +1963,7 @@ The following options are specific to the PowerPC emulation:
 
 @item -g @var{W}x@var{H}[x@var{DEPTH}]
 
-Set the initial VGA graphic mode. The default is 800x600x15.
+Set the initial VGA graphic mode. The default is 800x600x32.
 
 @item -prom-env @var{string}