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author Javier Rojas <jerojasro@devnull.li>
date Mon Jan 05 23:55:35 2009 -0500 (2009-01-05)
parents 6cf30b3ed48f
children b1ae672fd92b
rev   line source
jerojasro@481 1 \chapter{Usos avanzados de las Colas de Mercurial}
jerojasro@336 2 \label{chap:mq-collab}
jerojasro@336 3
jerojasro@481 4 Auunque es fácil aprender los usos más directos de las Colas de
jerojasro@481 5 Mercurial, tener algo de disciplina junto con algunas de las
jerojasro@481 6 capacidadees menos usadas de MQ hace posible trabajar en entornos de
jerojasro@481 7 desarrollo complejos.
jerojasro@481 8
jerojasro@481 9 En este capítulo, usaré como ejemplo una técnica que he usado para
jerojasro@481 10 administrar el desarrollo de un controlador de dispositivo Infiniband
jerojasro@481 11 para el kernel de Linux. El controlador en cuestión es grande
jerojasro@481 12 (al menos en lo que se refiere a controladores), con 25,000 líneas de
jerojasro@481 13 código esparcidas en 35 ficheros fuente. Es mantenido por un equipo
jerojasro@481 14 pequeño de desarrolladores.
jerojasro@481 15
jerojasro@481 16 Aunque mucho del material en este capítulo es específico de Linux, los
jerojasro@481 17 mismos principios aplican a cualquier base de código de la que usted
jerojasro@481 18 no sea el propietario principal, y sobre la que usted necesita hacer
jerojasro@481 19 un montón de desarrollo.
jerojasro@481 20
jerojasro@481 21 \section{El problema de múltiples objetivos}
jerojasro@481 22
jerojasro@481 23 El kernel de Linux cambia con rapidez, y nunca ha sido estable
jerojasro@481 24 internamente; los desarrolladores hacen cambios drásticos entre
jerojasro@481 25 %TODO no encontré una traducción adecuada para "release". Por eso el
jerojasro@481 26 %cambio
jerojasro@481 27 versiones frecuentemente. Esto significa que una versión del
jerojasro@481 28 controlador que funciona bien con una versión particular del kernel ni
jerojasro@481 29 siquiera \emph{compilará} correctamente contra, típicamente, cualquier
jerojasro@481 30 otra versión.
jerojasro@481 31
jerojasro@481 32 Para mantener un controlador, debemos tener en cuenta una buena
jerojasro@481 33 cantidad de versiones de Linux en mente.
jerojasro@336 34 \begin{itemize}
jerojasro@481 35 \item Un objetivo es el árbol de desarrollo principal del kernel de
jerojasro@481 36 Linux. En este caso el mantenimiento del código es compartido
jerojasro@481 37 parcialmente por otros desarrolladores en la comunidad del kernel,
jerojasro@481 38 %TODO drive-by.
jerojasro@481 39 quienes hacen modificaciones ``de-afán'' al controlador a medida que
jerojasro@481 40 desarrollan y refinan subsistemas en el kernel.
jerojasro@481 41 %TODO backport
jerojasro@481 42 \item También mantenemos algunos ``backports'' para versiones antiguas
jerojasro@481 43 del kernel de Linux, para dar soporte a las necesidades de los
jerojasro@481 44 clientes que están corriendo versiones antiguas de Linux que no
jerojasro@481 45 incorporan nuestros controladores. (Hacer el \emph{backport} de un
jerojasro@481 46 pedazo de código es modificarlo para que trabaje en una versión
jerojasro@481 47 de su entorno objetivo anterior a aquella para la cual fue escrito.)
jerojasro@481 48 \item Finalmente, nosotros liberamos nuestro software de acuerdo a un
jerojasro@481 49 cronograma que no necesariamente está alineado con el que usan los
jerojasro@481 50 distribuidores de Linux y los desarrolladores del kernel, así que
jerojasro@481 51 podemos entregar nuevas características a los clientes sin forzarlos
jerojasro@481 52 a actualizar kernels completos o distribuciones.
jerojasro@336 53 \end{itemize}
jerojasro@336 54
jerojasro@481 55 \subsection{Aproximaciones tentadoras que no funcionan adecuadamente}
jerojasro@481 56
jerojasro@481 57 Hay dos maneras estándar de mantener una porción de software que debe
jerojasro@481 58 funcionar en muchos entornos diferentes.
jerojasro@336 59
jerojasro@485 60 La primera es mantener varias ramas, cada una pensada para un único
jerojasro@485 61 entorno. El problema de esta aproximación es que usted debe tener una
jerojasro@485 62 disciplina férrea con el flujo de cambios entre repositorios. Una
jerojasro@485 63 nueva característica o un arreglo de fallo deben empezar su vida en un
jerojasro@485 64 repositorio ``prístino'', y luego propagarse a cada repositorio de
jerojasro@485 65 backport. Los cambios para backports están más limitados respecto a
jerojasro@485 66 las ramas a las que deberían propagarse; un cambio para backport que
jerojasro@485 67 es aplicado a una rama en la que no corresponde probablemente hará que
jerojasro@485 68 el controlador no compile.
jerojasro@485 69
jerojasro@485 70 La segunda es mantener un único árbol de código fuente lleno de
jerojasro@485 71 declaraciones que activen o desactiven secciones de código dependiendo
jerojasro@485 72 del entorno objetivo. Ya que estos ``ifdefs'' no están permitidos en
jerojasro@485 73 el árbol del kernel de Linux, debe seguirse algún proceso manual o
jerojasro@485 74 automático para eliminarlos y producir un árbol limpio. Una base de
jerojasro@485 75 código mantenida de esta manera se convierte rápidamente en un nido de
jerojasro@485 76 ratas de bloques condicionales que son difíciles de entender y
jerojasro@485 77 mantener.
jerojasro@485 78
jerojasro@485 79 %TODO canónica?
jerojasro@485 80 Ninguno de estos enfoques es adecuado para situaciones en las que
jerojasro@485 81 usted no es ``dueño'' de la copia canónica de un árbol de fuentes. En
jerojasro@485 82 el caso de un controlador de Linux que es distribuido con el kernel
jerojasro@485 83 estándar, el árbol de Linux contiene la copia del código que será
jerojasro@485 84 considerada por el mundo como la canónica. La versión oficial de
jerojasro@485 85 ``mi'' controlador puede ser modificada por gente que no conozco, sin
jerojasro@485 86 que yo siquiera me entere de ello hasta después de que los cambios
jerojasro@485 87 aparecen en el árbol de Linus.
jerojasro@485 88
jerojasro@485 89 Estos enfoques tienen la debilidad adicional de dificultar la
jerojasro@485 90 %TODO upstream. no no es río arriba
jerojasro@485 91 generación de parches bien formados para enviarlos a la versión
jerojasro@485 92 oficial.
jerojasro@485 93
jerojasro@485 94 En principio, las Colas de Mercurial parecen ser un buen candidato
jerojasro@485 95 para administrar un escenario de desarrollo como el de arriba. Aunque
jerojasro@485 96 este es de hecho el caso, MQ tiene unas cuantas características
jerojasro@485 97 adicionales que hacen el trabajo más agradable.
jerojasro@336 98
jerojasro@336 99 \section{Conditionally applying patches with
jerojasro@336 100 guards}
jerojasro@336 101
jerojasro@336 102 Perhaps the best way to maintain sanity with so many targets is to be
jerojasro@336 103 able to choose specific patches to apply for a given situation. MQ
jerojasro@336 104 provides a feature called ``guards'' (which originates with quilt's
jerojasro@336 105 \texttt{guards} command) that does just this. To start off, let's
jerojasro@336 106 create a simple repository for experimenting in.
jerojasro@336 107 \interaction{mq.guards.init}
jerojasro@336 108 This gives us a tiny repository that contains two patches that don't
jerojasro@336 109 have any dependencies on each other, because they touch different files.
jerojasro@336 110
jerojasro@336 111 The idea behind conditional application is that you can ``tag'' a
jerojasro@336 112 patch with a \emph{guard}, which is simply a text string of your
jerojasro@336 113 choosing, then tell MQ to select specific guards to use when applying
jerojasro@336 114 patches. MQ will then either apply, or skip over, a guarded patch,
jerojasro@336 115 depending on the guards that you have selected.
jerojasro@336 116
jerojasro@336 117 A patch can have an arbitrary number of guards;
jerojasro@336 118 each one is \emph{positive} (``apply this patch if this guard is
jerojasro@336 119 selected'') or \emph{negative} (``skip this patch if this guard is
jerojasro@336 120 selected''). A patch with no guards is always applied.
jerojasro@336 121
jerojasro@336 122 \section{Controlling the guards on a patch}
jerojasro@336 123
jerojasro@336 124 The \hgxcmd{mq}{qguard} command lets you determine which guards should
jerojasro@336 125 apply to a patch, or display the guards that are already in effect.
jerojasro@336 126 Without any arguments, it displays the guards on the current topmost
jerojasro@336 127 patch.
jerojasro@336 128 \interaction{mq.guards.qguard}
jerojasro@336 129 To set a positive guard on a patch, prefix the name of the guard with
jerojasro@336 130 a ``\texttt{+}''.
jerojasro@336 131 \interaction{mq.guards.qguard.pos}
jerojasro@336 132 To set a negative guard on a patch, prefix the name of the guard with
jerojasro@336 133 a ``\texttt{-}''.
jerojasro@336 134 \interaction{mq.guards.qguard.neg}
jerojasro@336 135
jerojasro@336 136 \begin{note}
jerojasro@336 137 The \hgxcmd{mq}{qguard} command \emph{sets} the guards on a patch; it
jerojasro@336 138 doesn't \emph{modify} them. What this means is that if you run
jerojasro@336 139 \hgcmdargs{qguard}{+a +b} on a patch, then \hgcmdargs{qguard}{+c} on
jerojasro@336 140 the same patch, the \emph{only} guard that will be set on it
jerojasro@336 141 afterwards is \texttt{+c}.
jerojasro@336 142 \end{note}
jerojasro@336 143
jerojasro@336 144 Mercurial stores guards in the \sfilename{series} file; the form in
jerojasro@336 145 which they are stored is easy both to understand and to edit by hand.
jerojasro@336 146 (In other words, you don't have to use the \hgxcmd{mq}{qguard} command if
jerojasro@336 147 you don't want to; it's okay to simply edit the \sfilename{series}
jerojasro@336 148 file.)
jerojasro@336 149 \interaction{mq.guards.series}
jerojasro@336 150
jerojasro@336 151 \section{Selecting the guards to use}
jerojasro@336 152
jerojasro@336 153 The \hgxcmd{mq}{qselect} command determines which guards are active at a
jerojasro@336 154 given time. The effect of this is to determine which patches MQ will
jerojasro@336 155 apply the next time you run \hgxcmd{mq}{qpush}. It has no other effect; in
jerojasro@336 156 particular, it doesn't do anything to patches that are already
jerojasro@336 157 applied.
jerojasro@336 158
jerojasro@336 159 With no arguments, the \hgxcmd{mq}{qselect} command lists the guards
jerojasro@336 160 currently in effect, one per line of output. Each argument is treated
jerojasro@336 161 as the name of a guard to apply.
jerojasro@336 162 \interaction{mq.guards.qselect.foo}
jerojasro@336 163 In case you're interested, the currently selected guards are stored in
jerojasro@336 164 the \sfilename{guards} file.
jerojasro@336 165 \interaction{mq.guards.qselect.cat}
jerojasro@336 166 We can see the effect the selected guards have when we run
jerojasro@336 167 \hgxcmd{mq}{qpush}.
jerojasro@336 168 \interaction{mq.guards.qselect.qpush}
jerojasro@336 169
jerojasro@336 170 A guard cannot start with a ``\texttt{+}'' or ``\texttt{-}''
jerojasro@336 171 character. The name of a guard must not contain white space, but most
jerojasro@336 172 other characters are acceptable. If you try to use a guard with an
jerojasro@336 173 invalid name, MQ will complain:
jerojasro@336 174 \interaction{mq.guards.qselect.error}
jerojasro@336 175 Changing the selected guards changes the patches that are applied.
jerojasro@336 176 \interaction{mq.guards.qselect.quux}
jerojasro@336 177 You can see in the example below that negative guards take precedence
jerojasro@336 178 over positive guards.
jerojasro@336 179 \interaction{mq.guards.qselect.foobar}
jerojasro@336 180
jerojasro@336 181 \section{MQ's rules for applying patches}
jerojasro@336 182
jerojasro@336 183 The rules that MQ uses when deciding whether to apply a patch
jerojasro@336 184 are as follows.
jerojasro@336 185 \begin{itemize}
jerojasro@336 186 \item A patch that has no guards is always applied.
jerojasro@336 187 \item If the patch has any negative guard that matches any currently
jerojasro@336 188 selected guard, the patch is skipped.
jerojasro@336 189 \item If the patch has any positive guard that matches any currently
jerojasro@336 190 selected guard, the patch is applied.
jerojasro@336 191 \item If the patch has positive or negative guards, but none matches
jerojasro@336 192 any currently selected guard, the patch is skipped.
jerojasro@336 193 \end{itemize}
jerojasro@336 194
jerojasro@336 195 \section{Trimming the work environment}
jerojasro@336 196
jerojasro@336 197 In working on the device driver I mentioned earlier, I don't apply the
jerojasro@336 198 patches to a normal Linux kernel tree. Instead, I use a repository
jerojasro@336 199 that contains only a snapshot of the source files and headers that are
jerojasro@336 200 relevant to Infiniband development. This repository is~1\% the size
jerojasro@336 201 of a kernel repository, so it's easier to work with.
jerojasro@336 202
jerojasro@336 203 I then choose a ``base'' version on top of which the patches are
jerojasro@336 204 applied. This is a snapshot of the Linux kernel tree as of a revision
jerojasro@336 205 of my choosing. When I take the snapshot, I record the changeset ID
jerojasro@336 206 from the kernel repository in the commit message. Since the snapshot
jerojasro@336 207 preserves the ``shape'' and content of the relevant parts of the
jerojasro@336 208 kernel tree, I can apply my patches on top of either my tiny
jerojasro@336 209 repository or a normal kernel tree.
jerojasro@336 210
jerojasro@336 211 Normally, the base tree atop which the patches apply should be a
jerojasro@336 212 snapshot of a very recent upstream tree. This best facilitates the
jerojasro@336 213 development of patches that can easily be submitted upstream with few
jerojasro@336 214 or no modifications.
jerojasro@336 215
jerojasro@336 216 \section{Dividing up the \sfilename{series} file}
jerojasro@336 217
jerojasro@336 218 I categorise the patches in the \sfilename{series} file into a number
jerojasro@336 219 of logical groups. Each section of like patches begins with a block
jerojasro@336 220 of comments that describes the purpose of the patches that follow.
jerojasro@336 221
jerojasro@336 222 The sequence of patch groups that I maintain follows. The ordering of
jerojasro@336 223 these groups is important; I'll describe why after I introduce the
jerojasro@336 224 groups.
jerojasro@336 225 \begin{itemize}
jerojasro@336 226 \item The ``accepted'' group. Patches that the development team has
jerojasro@336 227 submitted to the maintainer of the Infiniband subsystem, and which
jerojasro@336 228 he has accepted, but which are not present in the snapshot that the
jerojasro@336 229 tiny repository is based on. These are ``read only'' patches,
jerojasro@336 230 present only to transform the tree into a similar state as it is in
jerojasro@336 231 the upstream maintainer's repository.
jerojasro@336 232 \item The ``rework'' group. Patches that I have submitted, but that
jerojasro@336 233 the upstream maintainer has requested modifications to before he
jerojasro@336 234 will accept them.
jerojasro@336 235 \item The ``pending'' group. Patches that I have not yet submitted to
jerojasro@336 236 the upstream maintainer, but which we have finished working on.
jerojasro@336 237 These will be ``read only'' for a while. If the upstream maintainer
jerojasro@336 238 accepts them upon submission, I'll move them to the end of the
jerojasro@336 239 ``accepted'' group. If he requests that I modify any, I'll move
jerojasro@336 240 them to the beginning of the ``rework'' group.
jerojasro@336 241 \item The ``in progress'' group. Patches that are actively being
jerojasro@336 242 developed, and should not be submitted anywhere yet.
jerojasro@336 243 \item The ``backport'' group. Patches that adapt the source tree to
jerojasro@336 244 older versions of the kernel tree.
jerojasro@336 245 \item The ``do not ship'' group. Patches that for some reason should
jerojasro@336 246 never be submitted upstream. For example, one such patch might
jerojasro@336 247 change embedded driver identification strings to make it easier to
jerojasro@336 248 distinguish, in the field, between an out-of-tree version of the
jerojasro@336 249 driver and a version shipped by a distribution vendor.
jerojasro@336 250 \end{itemize}
jerojasro@336 251
jerojasro@336 252 Now to return to the reasons for ordering groups of patches in this
jerojasro@336 253 way. We would like the lowest patches in the stack to be as stable as
jerojasro@336 254 possible, so that we will not need to rework higher patches due to
jerojasro@336 255 changes in context. Putting patches that will never be changed first
jerojasro@336 256 in the \sfilename{series} file serves this purpose.
jerojasro@336 257
jerojasro@336 258 We would also like the patches that we know we'll need to modify to be
jerojasro@336 259 applied on top of a source tree that resembles the upstream tree as
jerojasro@336 260 closely as possible. This is why we keep accepted patches around for
jerojasro@336 261 a while.
jerojasro@336 262
jerojasro@336 263 The ``backport'' and ``do not ship'' patches float at the end of the
jerojasro@336 264 \sfilename{series} file. The backport patches must be applied on top
jerojasro@336 265 of all other patches, and the ``do not ship'' patches might as well
jerojasro@336 266 stay out of harm's way.
jerojasro@336 267
jerojasro@336 268 \section{Maintaining the patch series}
jerojasro@336 269
jerojasro@336 270 In my work, I use a number of guards to control which patches are to
jerojasro@336 271 be applied.
jerojasro@336 272
jerojasro@336 273 \begin{itemize}
jerojasro@336 274 \item ``Accepted'' patches are guarded with \texttt{accepted}. I
jerojasro@336 275 enable this guard most of the time. When I'm applying the patches
jerojasro@336 276 on top of a tree where the patches are already present, I can turn
jerojasro@336 277 this patch off, and the patches that follow it will apply cleanly.
jerojasro@336 278 \item Patches that are ``finished'', but not yet submitted, have no
jerojasro@336 279 guards. If I'm applying the patch stack to a copy of the upstream
jerojasro@336 280 tree, I don't need to enable any guards in order to get a reasonably
jerojasro@336 281 safe source tree.
jerojasro@336 282 \item Those patches that need reworking before being resubmitted are
jerojasro@336 283 guarded with \texttt{rework}.
jerojasro@336 284 \item For those patches that are still under development, I use
jerojasro@336 285 \texttt{devel}.
jerojasro@336 286 \item A backport patch may have several guards, one for each version
jerojasro@336 287 of the kernel to which it applies. For example, a patch that
jerojasro@336 288 backports a piece of code to~2.6.9 will have a~\texttt{2.6.9} guard.
jerojasro@336 289 \end{itemize}
jerojasro@336 290 This variety of guards gives me considerable flexibility in
jerojasro@336 291 qdetermining what kind of source tree I want to end up with. For most
jerojasro@336 292 situations, the selection of appropriate guards is automated during
jerojasro@336 293 the build process, but I can manually tune the guards to use for less
jerojasro@336 294 common circumstances.
jerojasro@336 295
jerojasro@336 296 \subsection{The art of writing backport patches}
jerojasro@336 297
jerojasro@336 298 Using MQ, writing a backport patch is a simple process. All such a
jerojasro@336 299 patch has to do is modify a piece of code that uses a kernel feature
jerojasro@336 300 not present in the older version of the kernel, so that the driver
jerojasro@336 301 continues to work correctly under that older version.
jerojasro@336 302
jerojasro@336 303 A useful goal when writing a good backport patch is to make your code
jerojasro@336 304 look as if it was written for the older version of the kernel you're
jerojasro@336 305 targeting. The less obtrusive the patch, the easier it will be to
jerojasro@336 306 understand and maintain. If you're writing a collection of backport
jerojasro@336 307 patches to avoid the ``rat's nest'' effect of lots of
jerojasro@336 308 \texttt{\#ifdef}s (hunks of source code that are only used
jerojasro@336 309 conditionally) in your code, don't introduce version-dependent
jerojasro@336 310 \texttt{\#ifdef}s into the patches. Instead, write several patches,
jerojasro@336 311 each of which makes unconditional changes, and control their
jerojasro@336 312 application using guards.
jerojasro@336 313
jerojasro@336 314 There are two reasons to divide backport patches into a distinct
jerojasro@336 315 group, away from the ``regular'' patches whose effects they modify.
jerojasro@336 316 The first is that intermingling the two makes it more difficult to use
jerojasro@336 317 a tool like the \hgext{patchbomb} extension to automate the process of
jerojasro@336 318 submitting the patches to an upstream maintainer. The second is that
jerojasro@336 319 a backport patch could perturb the context in which a subsequent
jerojasro@336 320 regular patch is applied, making it impossible to apply the regular
jerojasro@336 321 patch cleanly \emph{without} the earlier backport patch already being
jerojasro@336 322 applied.
jerojasro@336 323
jerojasro@336 324 \section{Useful tips for developing with MQ}
jerojasro@336 325
jerojasro@336 326 \subsection{Organising patches in directories}
jerojasro@336 327
jerojasro@336 328 If you're working on a substantial project with MQ, it's not difficult
jerojasro@336 329 to accumulate a large number of patches. For example, I have one
jerojasro@336 330 patch repository that contains over 250 patches.
jerojasro@336 331
jerojasro@336 332 If you can group these patches into separate logical categories, you
jerojasro@336 333 can if you like store them in different directories; MQ has no
jerojasro@336 334 problems with patch names that contain path separators.
jerojasro@336 335
jerojasro@336 336 \subsection{Viewing the history of a patch}
jerojasro@336 337 \label{mq-collab:tips:interdiff}
jerojasro@336 338
jerojasro@336 339 If you're developing a set of patches over a long time, it's a good
jerojasro@336 340 idea to maintain them in a repository, as discussed in
jerojasro@336 341 section~\ref{sec:mq:repo}. If you do so, you'll quickly discover that
jerojasro@336 342 using the \hgcmd{diff} command to look at the history of changes to a
jerojasro@336 343 patch is unworkable. This is in part because you're looking at the
jerojasro@336 344 second derivative of the real code (a diff of a diff), but also
jerojasro@336 345 because MQ adds noise to the process by modifying time stamps and
jerojasro@336 346 directory names when it updates a patch.
jerojasro@336 347
jerojasro@336 348 However, you can use the \hgext{extdiff} extension, which is bundled
jerojasro@336 349 with Mercurial, to turn a diff of two versions of a patch into
jerojasro@336 350 something readable. To do this, you will need a third-party package
jerojasro@336 351 called \package{patchutils}~\cite{web:patchutils}. This provides a
jerojasro@336 352 command named \command{interdiff}, which shows the differences between
jerojasro@336 353 two diffs as a diff. Used on two versions of the same diff, it
jerojasro@336 354 generates a diff that represents the diff from the first to the second
jerojasro@336 355 version.
jerojasro@336 356
jerojasro@336 357 You can enable the \hgext{extdiff} extension in the usual way, by
jerojasro@336 358 adding a line to the \rcsection{extensions} section of your \hgrc.
jerojasro@336 359 \begin{codesample2}
jerojasro@336 360 [extensions]
jerojasro@336 361 extdiff =
jerojasro@336 362 \end{codesample2}
jerojasro@336 363 The \command{interdiff} command expects to be passed the names of two
jerojasro@336 364 files, but the \hgext{extdiff} extension passes the program it runs a
jerojasro@336 365 pair of directories, each of which can contain an arbitrary number of
jerojasro@336 366 files. We thus need a small program that will run \command{interdiff}
jerojasro@336 367 on each pair of files in these two directories. This program is
jerojasro@336 368 available as \sfilename{hg-interdiff} in the \dirname{examples}
jerojasro@336 369 directory of the source code repository that accompanies this book.
jerojasro@336 370 \excode{hg-interdiff}
jerojasro@336 371
jerojasro@336 372 With the \sfilename{hg-interdiff} program in your shell's search path,
jerojasro@336 373 you can run it as follows, from inside an MQ patch directory:
jerojasro@336 374 \begin{codesample2}
jerojasro@336 375 hg extdiff -p hg-interdiff -r A:B my-change.patch
jerojasro@336 376 \end{codesample2}
jerojasro@336 377 Since you'll probably want to use this long-winded command a lot, you
jerojasro@336 378 can get \hgext{hgext} to make it available as a normal Mercurial
jerojasro@336 379 command, again by editing your \hgrc.
jerojasro@336 380 \begin{codesample2}
jerojasro@336 381 [extdiff]
jerojasro@336 382 cmd.interdiff = hg-interdiff
jerojasro@336 383 \end{codesample2}
jerojasro@336 384 This directs \hgext{hgext} to make an \texttt{interdiff} command
jerojasro@336 385 available, so you can now shorten the previous invocation of
jerojasro@336 386 \hgxcmd{extdiff}{extdiff} to something a little more wieldy.
jerojasro@336 387 \begin{codesample2}
jerojasro@336 388 hg interdiff -r A:B my-change.patch
jerojasro@336 389 \end{codesample2}
jerojasro@336 390
jerojasro@336 391 \begin{note}
jerojasro@336 392 The \command{interdiff} command works well only if the underlying
jerojasro@336 393 files against which versions of a patch are generated remain the
jerojasro@336 394 same. If you create a patch, modify the underlying files, and then
jerojasro@336 395 regenerate the patch, \command{interdiff} may not produce useful
jerojasro@336 396 output.
jerojasro@336 397 \end{note}
jerojasro@336 398
jerojasro@336 399 The \hgext{extdiff} extension is useful for more than merely improving
jerojasro@336 400 the presentation of MQ~patches. To read more about it, go to
jerojasro@336 401 section~\ref{sec:hgext:extdiff}.
jerojasro@336 402
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