target-i386: Rewrite gen_enter inline

[qemu.git] / qemu-img.texi

diff --git a/qemu-img.texi b/qemu-img.texi
index f86a86d916ab3f00579587c9051967ed630787db..7163a108e26fc85ac0b94971b3b6131ab4707f77 100644 (file)
--- a/qemu-img.texi
+++ b/qemu-img.texi
@@ -1,6 +1,6 @@
 @example
 @c man begin SYNOPSIS
 @example
 @c man begin SYNOPSIS

-usage: qemu-img command [command options]
+@command{qemu-img} @var{command} [@var{command} @var{options}]

 @c man end
 @end example
 
 @c man end
 @end example
 


@@ -72,6 +72,10 @@ down to the nearest 512 bytes. You may use the common size suffixes like
 specifies the cache mode that should be used with the (destination) file. See
 the documentation of the emulator's @code{-drive cache=...} option for allowed
 values.
 specifies the cache mode that should be used with the (destination) file. See
 the documentation of the emulator's @code{-drive cache=...} option for allowed
 values.

+@item -T @var{src_cache}
+specifies the cache mode that should be used with the source file(s). See
+the documentation of the emulator's @code{-drive cache=...} option for allowed
+values.

 @end table
 
 Parameters to snapshot subcommand:
 @end table
 
 Parameters to snapshot subcommand:


@@ -99,7 +103,7 @@ First image format
 @item -F
 Second image format
 @item -s
 @item -F
 Second image format
 @item -s

-Strict mode - fail on on different image size or sector allocation
+Strict mode - fail on different image size or sector allocation

 @end table
 
 Parameters to convert subcommand:
 @end table
 
 Parameters to convert subcommand:


@@ -113,7 +117,7 @@ Skip the creation of the target volume
 Command description:
 
 @table @option
 Command description:
 
 @table @option

-@item check [-f @var{fmt}] [--output=@var{ofmt}] [-r [leaks | all]] @var{filename}
+@item check [-f @var{fmt}] [--output=@var{ofmt}] [-r [leaks | all]] [-T @var{src_cache}] @var{filename}

 
 Perform a consistency check on the disk image @var{filename}. The command can
 output in the format @var{ofmt} which is either @code{human} or @code{json}.
 
 Perform a consistency check on the disk image @var{filename}. The command can
 output in the format @var{ofmt} which is either @code{human} or @code{json}.


@@ -126,6 +130,29 @@ wrong fix or hiding corruption that has already occurred.
 Only the formats @code{qcow2}, @code{qed} and @code{vdi} support
 consistency checks.
 
 Only the formats @code{qcow2}, @code{qed} and @code{vdi} support
 consistency checks.
 

+In case the image does not have any inconsistencies, check exits with @code{0}.
+Other exit codes indicate the kind of inconsistency found or if another error
+occurred. The following table summarizes all exit codes of the check subcommand:
+
+@table @option
+
+@item 0
+Check completed, the image is (now) consistent
+@item 1
+Check not completed because of internal errors
+@item 2
+Check completed, image is corrupted
+@item 3
+Check completed, image has leaked clusters, but is not corrupted
+@item 63
+Checks are not supported by the image format
+
+@end table
+
+If @code{-r} is specified, exit codes representing the image state refer to the
+state after (the attempt at) repairing it. That is, a successful @code{-r all}
+will yield the exit code 0, independently of the image state before.
+

 @item create [-f @var{fmt}] [-o @var{options}] @var{filename} [@var{size}]
 
 Create the new disk image @var{filename} of size @var{size} and format
 @item create [-f @var{fmt}] [-o @var{options}] @var{filename} [@var{size}]
 
 Create the new disk image @var{filename} of size @var{size} and format


@@ -140,11 +167,30 @@ this case. @var{backing_file} will never be modified unless you use the
 The size can also be specified using the @var{size} option with @code{-o},
 it doesn't need to be specified separately in this case.
 
 The size can also be specified using the @var{size} option with @code{-o},
 it doesn't need to be specified separately in this case.
 

-@item commit [-f @var{fmt}] [-t @var{cache}] @var{filename}
+@item commit [-q] [-f @var{fmt}] [-t @var{cache}] [-b @var{base}] [-d] [-p] @var{filename}

 
 

-Commit the changes recorded in @var{filename} in its base image.
+Commit the changes recorded in @var{filename} in its base image or backing file.
+If the backing file is smaller than the snapshot, then the backing file will be
+resized to be the same size as the snapshot.  If the snapshot is smaller than
+the backing file, the backing file will not be truncated.  If you want the
+backing file to match the size of the smaller snapshot, you can safely truncate
+it yourself once the commit operation successfully completes.

 
 

-@item compare [-f @var{fmt}] [-F @var{fmt}] [-p] [-s] [-q] @var{filename1} @var{filename2}
+The image @var{filename} is emptied after the operation has succeeded. If you do
+not need @var{filename} afterwards and intend to drop it, you may skip emptying
+@var{filename} by specifying the @code{-d} flag.
+
+If the backing chain of the given image file @var{filename} has more than one
+layer, the backing file into which the changes will be committed may be
+specified as @var{base} (which has to be part of @var{filename}'s backing
+chain). If @var{base} is not specified, the immediate backing file of the top
+image (which is @var{filename}) will be used. For reasons of consistency,
+explicitly specifying @var{base} will always imply @code{-d} (since emptying an
+image after committing to an indirect backing file would lead to different data
+being read from the image due to content in the intermediate backing chain
+overruling the commit target).
+
+@item compare [-f @var{fmt}] [-F @var{fmt}] [-T @var{src_cache}] [-p] [-s] [-q] @var{filename1} @var{filename2}

 
 Check if two images have the same content. You can compare images with
 different format or settings.
 
 Check if two images have the same content. You can compare images with
 different format or settings.


@@ -185,7 +231,7 @@ Error on reading data
 
 @end table
 
 
 @end table
 

-@item convert [-c] [-p] [-n] [-f @var{fmt}] [-t @var{cache}] [-O @var{output_fmt}] [-o @var{options}] [-s @var{snapshot_id_or_name}] [-l @var{snapshot_param}] [-S @var{sparse_size}] @var{filename} [@var{filename2} [...]] @var{output_filename}
+@item convert [-c] [-p] [-n] [-f @var{fmt}] [-t @var{cache}] [-T @var{src_cache}] [-O @var{output_fmt}] [-o @var{options}] [-s @var{snapshot_id_or_name}] [-l @var{snapshot_param}] [-S @var{sparse_size}] @var{filename} [@var{filename2} [...]] @var{output_filename}

 
 Convert the disk image @var{filename} or a snapshot @var{snapshot_param}(@var{snapshot_id_or_name} is deprecated)
 to disk image @var{output_filename} using format @var{output_fmt}. It can be optionally compressed (@code{-c}
 
 Convert the disk image @var{filename} or a snapshot @var{snapshot_param}(@var{snapshot_id_or_name} is deprecated)
 to disk image @var{output_filename} using format @var{output_fmt}. It can be optionally compressed (@code{-c}


@@ -196,8 +242,8 @@ compression is read-only. It means that if a compressed sector is
 rewritten, then it is rewritten as uncompressed data.
 
 Image conversion is also useful to get smaller image when using a
 rewritten, then it is rewritten as uncompressed data.
 
 Image conversion is also useful to get smaller image when using a

-growable format such as @code{qcow} or @code{cow}: the empty sectors
-are detected and suppressed from the destination image.
+growable format such as @code{qcow}: the empty sectors are detected and
+suppressed from the destination image.

 
 @var{sparse_size} indicates the consecutive number of bytes (defaults to 4k)
 that must contain only zeros for qemu-img to create a sparse image during
 
 @var{sparse_size} indicates the consecutive number of bytes (defaults to 4k)
 that must contain only zeros for qemu-img to create a sparse image during


@@ -297,7 +343,7 @@ source code.
 
 List, apply, create or delete snapshots in image @var{filename}.
 
 
 List, apply, create or delete snapshots in image @var{filename}.
 

-@item rebase [-f @var{fmt}] [-t @var{cache}] [-p] [-u] -b @var{backing_file} [-F @var{backing_fmt}] @var{filename}
+@item rebase [-f @var{fmt}] [-t @var{cache}] [-T @var{src_cache}] [-p] [-u] -b @var{backing_file} [-F @var{backing_fmt}] @var{filename}

 
 Changes the backing file of an image. Only the formats @code{qcow2} and
 @code{qed} support changing the backing file.
 
 Changes the backing file of an image. Only the formats @code{qcow2} and
 @code{qed} support changing the backing file.


@@ -308,6 +354,9 @@ The backing file is changed to @var{backing_file} and (if the image format of
 string), then the image is rebased onto no backing file (i.e. it will exist
 independently of any backing file).
 
 string), then the image is rebased onto no backing file (i.e. it will exist
 independently of any backing file).
 

+@var{cache} specifies the cache mode to be used for @var{filename}, whereas
+@var{src_cache} specifies the cache mode for reading backing files.
+

 There are two different modes in which @code{rebase} can operate:
 @table @option
 @item Safe mode
 There are two different modes in which @code{rebase} can operate:
 @table @option
 @item Safe mode


@@ -363,7 +412,7 @@ After using this command to grow a disk image, you must use file system and
 partitioning tools inside the VM to actually begin using the new space on the
 device.
 
 partitioning tools inside the VM to actually begin using the new space on the
 device.
 

-@item amend [-f @var{fmt}] -o @var{options} @var{filename}
+@item amend [-p] [-f @var{fmt}] [-t @var{cache}] -o @var{options} @var{filename}

 
 Amends the image format specific @var{options} for the image file
 @var{filename}. Not all file formats support this operation.
 
 Amends the image format specific @var{options} for the image file
 @var{filename}. Not all file formats support this operation.


@@ -384,6 +433,15 @@ 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.
 
 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
 @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


@@ -404,10 +462,27 @@ File name of a base image (see @option{create} subcommand)
 @item backing_fmt
 Image format of the base image
 @item encryption
 @item backing_fmt
 Image format of the base image
 @item encryption

-If this option is set to @code{on}, the image is encrypted.
+If this option is set to @code{on}, the image is encrypted with 128-bit AES-CBC.
+
+The use of encryption in qcow and qcow2 images is considered to be flawed by
+modern cryptography standards, suffering from a number of design problems:
+
+@itemize @minus
+@item The AES-CBC cipher is used with predictable initialization vectors based
+on the sector number. This makes it vulnerable to chosen plaintext attacks
+which can reveal the existence of encrypted data.
+@item The user passphrase is directly used as the encryption key. A poorly
+chosen or short passphrase will compromise the security of the encryption.
+@item In the event of the passphrase being compromised there is no way to
+change the passphrase to protect data in any qcow images. The files must
+be cloned, using a different encryption passphrase in the new file. The
+original file must then be securely erased using a program like shred,
+though even this is ineffective with many modern storage technologies.
+@end itemize

 
 

-Encryption uses the AES format which is very secure (128 bit keys). Use
-a long password (16 characters) to get maximum protection.
+Use of qcow / qcow2 encryption is thus strongly discouraged. Users are
+recommended to use an alternative encryption technology such as the
+Linux dm-crypt / LUKS system.

 
 @item cluster_size
 Changes the qcow2 cluster size (must be between 512 and 2M). Smaller cluster
 
 @item cluster_size
 Changes the qcow2 cluster size (must be between 512 and 2M). Smaller cluster


@@ -415,9 +490,11 @@ sizes can improve the image file size whereas larger cluster sizes generally
 provide better performance.
 
 @item preallocation
 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
 
 @item lazy_refcounts
 If this option is set to @code{on}, reference count updates are postponed with


@@ -429,6 +506,22 @@ check -r all} is required, which may take some time.
 
 This option can only be enabled if @code{compat=1.1} is specified.
 
 
 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 Other
 @end table
 
 @item Other