[CI:DOCS] elaborate on image lookups of foreign platforms

After pulling/creating an image of a foreign platform, Podman will
happily use it when looking it up in the local storage and will not
pull down the image matching the host platform.

As discussed in #12682, the reasoning for it is Docker compatibility and
the fact that user already rely on the behavior.  While Podman is now
emitting a warning when an image is in use not matching the local
platform, the documentation was lacking that information.

Fixes: #15300
Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>

1 files changed, 11 insertions, 6 deletions

diff --git a/docs/source/markdown/podman-build.1.md.in b/docs/source/markdown/podman-build.1.md.in
index b49beb3bf..350930adf 100644
--- a/docs/source/markdown/podman-build.1.md.in
+++ b/docs/source/markdown/podman-build.1.md.in
@@ -65,8 +65,9 @@ discarded when writing images in Docker formats.
 
 Set the architecture of the image to be built, and that of the base image to be
 pulled, if the build uses one, to the provided value instead of using the
-architecture of the build host. (Examples: arm, arm64, 386, amd64, ppc64le,
-s390x)
+architecture of the build host. Unless overridden, subsequent lookups of the
+same image in the local storage will match this architecture, regardless of the
+host. (Examples: arm, arm64, 386, amd64, ppc64le, s390x)
 
 @@option authfile
 
@@ -454,7 +455,8 @@ do not include `History` information in their images.
 
 Set the OS of the image to be built, and that of the base image to be pulled,
 if the build uses one, instead of using the current operating system of the
-build host.
+build host. Unless overridden, subsequent lookups of the same image in the
+local storage will match this OS, regardless of the host.
 
 #### **--os-feature**=*feature*
 
@@ -506,9 +508,12 @@ process.
 
 Set the *os/arch* of the built image (and its base image, if your build uses one)
 to the provided value instead of using the current operating system and
-architecture of the host (for example `linux/arm`). If `--platform` is set,
-then the values of the `--arch`, `--os`, and `--variant` options will be
-overridden.
+architecture of the host (for example `linux/arm`).  Unless overridden,
+subsequent lookups of the same image in the local storage will match this
+platform, regardless of the host.
+
+If `--platform` is set, then the values of the `--arch`, `--os`, and
+`--variant` options will be overridden.
 
 The `--platform` option can be specified more than once, or given a
 comma-separated list of values as its argument.  When more than one platform is