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fs_mgr: Look for fstab file in /system/etc

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Look for the fstab file in /system/etc as an alternative to /, in order
to allow fstab files to be installed using the "prebuilt_etc" Soong
module.

This new path is meant to be used by the vendor ramdisk only. As before,
fstabs should *not* be placed in /system/etc on the system partition.

In more detail: sometimes, multiple nearly-identical fstabs need to be
installed to a device, with the correct one being selected at boot time
(b/191417025 as well as other cases that partners have run into).  To
avoid error-prone duplication of configuration files, these fstabs
should be generated from a template by the build system instead of being
duplicated in the source tree.  But if this is done, the usual way of
installing fstabs (PRODUCT_COPY_FILES) can't be used; they need to be
made into real build system modules instead.

Currently, the "prebuilt_etc" Soong module can't correctly install the
vendor_ramdisk copy of the fstab(s), since it will install it into the
/system/etc directory whereas Android currently requires that the
vendor_ramdisk copy of the fstab(s) be placed in the root directory.

Earlier I proposed adding a "prebuilt_fstab" module to handle this quirk
(https://r.android.com/1744033).  However, it was requested to instead
always look for the fstabs in /etc too, in order to allow "prebuilt_etc"
to be used and because /etc is the appropriate place for this file.
This change implements that suggestion (but actually using /system/etc,
since that is where "prebuilt_etc" actually installs it).

Bug: 191417025
Test: Tested that a device boots both with this, both before and after
      http://ag/15075136 which uses the new location.
Change-Id: Id083070e51ae85959167e4615cd96b31a0b1bd6a
This commit is contained in:
Eric Biggers 2021-07-29 19:04:41 -07:00
parent f204986802
commit e98afa2687
1 changed files with 12 additions and 5 deletions
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17
fs_mgr/fs_mgr_fstab.cpp
View file

@ -413,17 +413,24 @@ std::string ReadFstabFromDt() {
return fstab_result;
}
// Identify path to fstab file. Lookup is based on pattern
// fstab.<fstab_suffix>, fstab.<hardware>, fstab.<hardware.platform> in
// folders /odm/etc, vendor/etc, or /.
// Return the path to the fstab file. There may be multiple fstab files; the
// one that is returned will be the first that exists of fstab.<fstab_suffix>,
// fstab.<hardware>, and fstab.<hardware.platform>. The fstab is searched for
// in /odm/etc/ and /vendor/etc/, as well as in the locations where it may be in
// the first stage ramdisk during early boot. Previously, the first stage
// ramdisk's copy of the fstab had to be located in the root directory, but now
// the system/etc directory is supported too and is the preferred location.
std::string GetFstabPath() {
for (const char* prop : {"fstab_suffix", "hardware", "hardware.platform"}) {
std::string suffix;
if (!fs_mgr_get_boot_config(prop, &suffix)) continue;
for (const char* prefix :
{"/odm/etc/fstab.", "/vendor/etc/fstab.", "/fstab.", "/first_stage_ramdisk/fstab."}) {
for (const char* prefix : {// late-boot/post-boot locations
"/odm/etc/fstab.", "/vendor/etc/fstab.",
// early boot locations
"/system/etc/fstab.", "/first_stage_ramdisk/system/etc/fstab.",
"/fstab.", "/first_stage_ramdisk/fstab."}) {
std::string fstab_path = prefix + suffix;
if (access(fstab_path.c_str(), F_OK) == 0) {
return fstab_path;