Yocto - copy file generated from one recipe to another recipe yocto - build

Question

I have two recipes, a.bb & b.bb. Now in a.bb do_install, I am creating a sample.txt file and placing it under ${S} of "a" (or if needed can be placed under ${D}. Now when b.bb executes, in its do_install, I need to access the sample.txt
a.bb
do_install () {
echo "sample" > ${S}/sample.txt
}
b.bb
do_install () {
//access sample.txt here
}
I have set DEPENDS such that a.bb will be executed before b.bb.. now any pointer to achieve the above scenario? in yocto manual I see references of STAGING_DIR*, but did not find any helpful example.

Answer 1

You can't access (reliably) temporary files from another package. Each package is built independently in its own "sandbox". If files from one package are needed for other packages they need to be exported in the sysroot.
Please generate sample.txt to sysroot using ${D} during do_install and then you can access it from in the specific path in sysroot.
a.bb
do_install () {
echo "sample" > ${D}${includedir}/sample.txt
}
b.bb
do_install () {
// action example
install -m 0644 ${D}${includedir}/sample.txt ${S}/sample_2.txt
}
The ${D} variable allows the software being built to be installed in a directory other than its real target.

Answer 2

It Depends on what you want to do. If you want to use header or library files from recipe a.bb, then you should add corresponding package of recipe a.bb to DEPENDS in b.bb. Now b.bb will automatically look for files from SYSROOT during compilation/installation.
Or if you just want to add some file/changes to source, then create .patch for change and add to SRC_URI in both the recipe's
a.bb
SRC_URI += "file://sample.patch"
b.bb
SRC_URI += "file://sample.patch"