[casaroli]

Summary

libc does not build popen(), pclose(), dpopen() and dpclose() when CONFIG_SYSTEM_POPEN selects the copy in apps/system/popen ([1/5] #20778). [4/5] apache/nuttx-apps#3890 removes that copy and the option from apps, so this PR removes the check from libs/libc/stdio and libs/libc/unistd (Make.defs and CMakeLists.txt).

The second commit removes the documentation page of apps/system/popen and describes the libc functions in a new page of the libc documentation: the options they need, the shell they start, and how they start a command when there is no shell.

Impact

No change for configurations without CONFIG_SYSTEM_POPEN, which are all configurations after [3/5] #20792 and [4/5]. With an older apps tree that still sets CONFIG_SYSTEM_POPEN=y, both copies are compiled; the link takes the apps copy, as before.

Testing

Built with [4/5] (apps); in each, libc builds lib_popen.o and lib_dpopen.o, and no option of the defconfig is lost after make olddefconfig:

Configuration	Result
qemu-armv8a:fastboot	builds, CONFIG_SYSTEM_FASTBOOTD_SHELL=y
sabre-6quad:citest, rv-virt:citest, rv-virt:citest64	build, CONFIG_EXAMPLES_POPEN=y
lx_cpu:nsh	builds
esp32s3-devkit:fastboot, :fastboot_tcp, :fastboot_usb, lckfb-szpi-esp32s3:fastboot, :fastboot_tcp, :fastboot_usb	build, CONFIG_SYSTEM_FASTBOOTD_SHELL=y
sim:citest, sim:quickjs (x86_64 Linux in Docker)	build, CONFIG_EXAMPLES_POPEN=y in sim:citest
qemu-intel64:citest_smp (x86_64 Linux in Docker)	builds, CONFIG_EXAMPLES_POPEN=y

sim:sqlite was not built: the build host has no tclsh, which the SQLite build needs.

Runtime on qemu-armv8a:knsh and qemu-armv8a:nsh (QEMU with HVF) with CONFIG_TESTING_POPEN and CONFIG_EXAMPLES_POPEN: popen_test ends with === Results: 0 failed === (8 tests), and the popen example reads the output of help and exits with 0.

With apps master (system/popen still present) and CONFIG_SYSTEM_POPEN=y on qemu-armv8a:nsh: both copies compile, the image links without errors and has one popen(), the apps copy.

tools/checkpatch.sh -c -u -m -g passes.

depends-on: [apache/nuttx-apps/pull/3890]

[github-actions]

MemBrowse Memory Report · Explore what changed →

qemu-armv8a

• Code: .text.hostfs_open +8 B, .text.nsh_builtin -64 B, .text.nsh_parse_command +24 B (-0.0%, 351,880 B)

qemu-intel64

• Code: .text -68 B (-0.0%, 8,685,677 B)

No memory changes detected for:

• arduino-mega2560
• esp32-devkitc
• hifive1-revb
• mirtoo
• rx65n-rsk2mb
• s698pm-dkit
• stm32-nucleo-f103rb

---

_{Catch memory regressions in CI with MemBrowse. Free for open source.}

[github-actions]

🔗 Cross-repo PR dependencies

The read-only Build run reported the following dependent PR(s) and fetched head SHA(s):

• [4/5] system/popen: Remove it and use the popen() of libc. nuttx-apps#3890 @ 05d0004792

CI run: https://github.com/apache/nuttx/actions/runs/39420528204

[github-actions]

🔗 Cross-repo PR dependencies

The read-only Build run reported the following dependent PR(s) and fetched head SHA(s):

• [4/5] system/popen: Remove it and use the popen() of libc. nuttx-apps#3890 @ 05d0004792

CI run: https://github.com/apache/nuttx/actions/runs/39563368119

[github-actions]

🔗 Cross-repo PR dependencies

The read-only Build run reported the following dependent PR(s) and fetched head SHA(s):

• [4/5] system/popen: Remove it and use the popen() of libc. nuttx-apps#3890 @ becc96df27

CI run: https://github.com/apache/nuttx/actions/runs/39773652187