Currently, exec_setup_credential always rewrite
all credentials on exec_invoke, i.e. each ExecCommand
invocation. This is problematic though:

* When writing tmp cred files, we essentially double
  the size of each credential. Therefore, if one cred
  is bigger than half of CREDENTIALS_TOTAL_SIZE_MAX,
  confusing error occurs (see also
  systemd#24734 (comment))

* Credential is a unit thing and should not change during
  the whole lifetime of the unit. However, if e.g. a
  on-disk credential or unit file (SetCredential=)
  changes between ExecStart= and ExecStartPost=,
  the credentials are overwritten and the main process
  is suddenly seeing completely different creds
  when ExecStartPost= gets executed.

So, let's always reuse final cred dir if mounted and
not empty, so that the creds used is stable and probably
more efficient.

Currently, exec_setup_credential always rewrite
all credentials on exec_invoke, i.e. each ExecCommand
invocation. This is problematic though:

* When writing tmp cred files, we essentially double
  the size of each credential. Therefore, if one cred
  is bigger than half of CREDENTIALS_TOTAL_SIZE_MAX,
  confusing error occurs (see also
  systemd#24734 (comment))

* Credential is a unit thing and should not change during
  the whole lifetime of the unit. However, if e.g. a
  on-disk credential or unit file (SetCredential=)
  changes between ExecStart= and ExecStartPost=,
  the credentials are overwritten and the main process
  is suddenly seeing completely different creds
  when ExecStartPost= gets executed.

So, let's always reuse final cred dir if mounted and
not empty, so that the creds used is stable and probably
more efficient.

Currently, exec_setup_credential always rewrite
all credentials on exec_invoke, i.e. each ExecCommand
invocation. This is problematic though:

* When writing tmp cred files, we essentially double
  the size of each credential. Therefore, if one cred
  is bigger than half of CREDENTIALS_TOTAL_SIZE_MAX,
  confusing error occurs (see also
  systemd#24734 (comment))

* Credential is a unit thing and should not change during
  the whole lifetime of the unit. However, if e.g. a
  on-disk credential or unit file (SetCredential=)
  changes between ExecStart= and ExecStartPost=,
  the credentials are overwritten and the main process
  is suddenly seeing completely different creds
  when ExecStartPost= gets executed.

So, let's always reuse final cred dir if mounted and
not empty, so that the creds used is stable and probably
more efficient.

Currently, exec_setup_credential always rewrite
all credentials on exec_invoke, i.e. each ExecCommand
invocation. This is problematic though:

* When writing tmp cred files, we essentially double
  the size of each credential. Therefore, if one cred
  is bigger than half of CREDENTIALS_TOTAL_SIZE_MAX,
  confusing error occurs (see also
  systemd#24734 (comment))

* Credential is a unit thing and should not change during
  the whole lifetime of the unit. However, if e.g. a
  on-disk credential or unit file (SetCredential=)
  changes between ExecStart= and ExecStartPost=,
  the credentials are overwritten and the main process
  is suddenly seeing completely different creds
  when ExecStartPost= gets executed.

So, let's always reuse final cred dir if mounted and
not empty, so that the creds used is stable and probably
more efficient.

Currently, exec_setup_credential always rewrite
all credentials on exec_invoke, i.e. each ExecCommand
invocation. This is problematic though:

* When writing tmp cred files, we essentially double
  the size of each credential. Therefore, if one cred
  is bigger than half of CREDENTIALS_TOTAL_SIZE_MAX,
  confusing error occurs (see also
  systemd#24734 (comment))

* Credential is a unit thing and should not change during
  the whole lifetime of the unit. However, if e.g. a
  on-disk credential or unit file (SetCredential=)
  changes between ExecStart= and ExecStartPost=,
  the credentials are overwritten and the main process
  is suddenly seeing completely different creds
  when ExecStartPost= gets executed.

So, let's always reuse final cred dir if mounted and
not empty, so that the creds used is stable and probably
more efficient.

Currently, exec_setup_credential always rewrite
all credentials on exec_invoke, i.e. each ExecCommand
invocation. This is problematic though:

* When writing tmp cred files, we essentially double
  the size of each credential. Therefore, if one cred
  is bigger than half of CREDENTIALS_TOTAL_SIZE_MAX,
  confusing error occurs (see also
  systemd#24734 (comment))

* Credential is a unit thing and should not change during
  the whole lifetime of the unit. However, if e.g. a
  on-disk credential or unit file (SetCredential=)
  changes between ExecStart= and ExecStartPost=,
  the credentials are overwritten and the main process
  is suddenly seeing completely different creds
  when ExecStartPost= gets executed.

So, let's always reuse final cred dir if mounted and
not empty, so that the creds used is stable and probably
more efficient.

Currently, exec_setup_credential always rewrite
all credentials on exec_invoke, i.e. each ExecCommand
invocation. This is problematic though:

* When writing tmp cred files, we essentially double
  the size of each credential. Therefore, if one cred
  is bigger than half of CREDENTIALS_TOTAL_SIZE_MAX,
  confusing error occurs (see also
  systemd#24734 (comment))

* Credential is a unit thing and should not change during
  the whole lifetime of the unit. However, if e.g. a
  on-disk credential or unit file (SetCredential=)
  changes between ExecStart= and ExecStartPost=,
  the credentials are overwritten and the main process
  is suddenly seeing completely different creds
  when ExecStartPost= gets executed.

So, let's always reuse final cred dir if mounted and
not empty, so that the creds used is stable and probably
more efficient.

Currently, exec_setup_credential() always rewrite all credentials
upon exec_invoke(), i.e. invocation of each ExecCommand. This is
problematic though:

* When writing each tmp cred file, we essentially double the size
  of the credential. Therefore, if one cred is bigger than half
  of CREDENTIALS_TOTAL_SIZE_MAX, confusing ENOSPC occurs (see also
  systemd#24734 (comment))

* Credential is a unit-wide thing and thus should not change
  during the whole lifetime of the unit. However, if e.g.
  a on-disk credential or SetCredential= in unit file
  changes between ExecStart= and ExecStartPost=,
  the credentials are overwritten when the latter gets to run,
  and the already-running main process is suddenly seeing
  completely different creds. This one is especially awkward IMO,
  say if people use a timer to regularly update local creds.

So, let's always reuse final cred dir if mounted and not empty,
so that the creds used is stable and each exec_invoke() is probably
more efficient.

fresh otherwise

Currently, exec_setup_credential() always rewrite all credentials
upon exec_invoke(), i.e. invocation of each ExecCommand, and within
a single tmpfs instance. This is problematic though:

* When writing each tmp cred file, we essentially double the size
  of the credential. Therefore, if one cred is bigger than half
  of CREDENTIALS_TOTAL_SIZE_MAX, confusing ENOSPC occurs (see also
  systemd#24734 (comment))

* Credential is a unit-wide thing and thus should not change
  during the whole lifetime of main process. However, if e.g.
  a on-disk credential or SetCredential= in unit file
  changes between ExecStart= and ExecStartPost=,
  the credentials are overwritten when the latter gets to run,
  and the already-running main process is suddenly seeing
  completely different creds.

So, let's try to reuse final cred dir if the main process has started
and the tmpfs has been populated, so that the creds used is stable
across all ExecStart= and ExecStartPost=-s. We still want to retain
the ability of updating creds through ExecStartPre= though, therefore
we forcibly use a fresh cred dir for those. 'Fresh' means to actually
unmount the old tmpfs first, so the first problem goes away, too.

fresh otherwise

Currently, exec_setup_credential() always rewrite all credentials
upon exec_invoke(), i.e. invocation of each ExecCommand, and within
a single tmpfs instance. This is problematic though:

* When writing each tmp cred file, we essentially double the size
  of the credential. Therefore, if one cred is bigger than half
  of CREDENTIALS_TOTAL_SIZE_MAX, confusing ENOSPC occurs (see also
  systemd#24734 (comment))

* Credential is a unit-wide thing and thus should not change
  during the whole lifetime of main process. However, if e.g.
  a on-disk credential or SetCredential= in unit file
  changes between ExecStart= and ExecStartPost=,
  the credentials are overwritten when the latter gets to run,
  and the already-running main process is suddenly seeing
  completely different creds.

So, let's try to reuse final cred dir if the main process has started
and the tmpfs has been populated, so that the creds used is stable
across all ExecStart= and ExecStartPost=-s. We still want to retain
the ability of updating creds through ExecStartPre= though, therefore
we forcibly use a fresh cred dir for those. 'Fresh' means to actually
unmount the old tmpfs first, so the first problem goes away, too.

fresh otherwise

Currently, exec_setup_credential() always rewrite all credentials
upon exec_invoke(), i.e. invocation of each ExecCommand, and within
a single tmpfs instance. This is problematic though:

* When writing each tmp cred file, we essentially double the size
  of the credential. Therefore, if one cred is bigger than half
  of CREDENTIALS_TOTAL_SIZE_MAX, confusing ENOSPC occurs (see also
  systemd#24734 (comment))

* Credential is a unit-wide thing and thus should not change
  during the whole lifetime of main process. However, if e.g.
  a on-disk credential or SetCredential= in unit file
  changes between ExecStart= and ExecStartPost=,
  the credentials are overwritten when the latter gets to run,
  and the already-running main process is suddenly seeing
  completely different creds.

So, let's try to reuse final cred dir if the main process has started
and the tmpfs has been populated, so that the creds used is stable
across all ExecStart= and ExecStartPost=-s. We still want to retain
the ability of updating creds through ExecStartPre= though, therefore
we forcibly use a fresh cred dir for those. 'Fresh' means to actually
unmount the old tmpfs first, so the first problem goes away, too.

fresh otherwise

Currently, exec_setup_credential() always rewrite all credentials
upon exec_invoke(), i.e. invocation of each ExecCommand, and within
a single tmpfs instance. This is problematic though:

* When writing each tmp cred file, we essentially double the size
  of the credential. Therefore, if one cred is bigger than half
  of CREDENTIALS_TOTAL_SIZE_MAX, confusing ENOSPC occurs (see also
  systemd#24734 (comment))

* Credential is a unit-wide thing and thus should not change
  during the whole lifetime of main process. However, if e.g.
  a on-disk credential or SetCredential= in unit file
  changes between ExecStart= and ExecStartPost=,
  the credentials are overwritten when the latter gets to run,
  and the already-running main process is suddenly seeing
  completely different creds.

So, let's try to reuse final cred dir if the main process has started
and the tmpfs has been populated, so that the creds used is stable
across all ExecStart= and ExecStartPost=-s. We still want to retain
the ability of updating creds through ExecStartPre= though, therefore
we forcibly use a fresh cred dir for those. 'Fresh' means to actually
unmount the old tmpfs first, so the first problem goes away, too.

fresh otherwise

Currently, exec_setup_credential() always rewrite all credentials
upon exec_invoke(), i.e. invocation of each ExecCommand, and within
a single tmpfs instance. This is problematic though:

* When writing each tmp cred file, we essentially double the size
  of the credential. Therefore, if one cred is bigger than half
  of CREDENTIALS_TOTAL_SIZE_MAX, confusing ENOSPC occurs (see also
  systemd#24734 (comment))

* Credential is a unit-wide thing and thus should not change
  during the whole lifetime of main process. However, if e.g.
  a on-disk credential or SetCredential= in unit file
  changes between ExecStart= and ExecStartPost=,
  the credentials are overwritten when the latter gets to run,
  and the already-running main process is suddenly seeing
  completely different creds.

So, let's try to reuse final cred dir if the main process has started
and the tmpfs has been populated, so that the creds used is stable
across all ExecStart= and ExecStartPost=-s. We still want to retain
the ability of updating creds through ExecStartPre= though, therefore
we forcibly use a fresh cred dir for those. 'Fresh' means to actually
unmount the old tmpfs first, so the first problem goes away, too.

fresh otherwise

Currently, exec_setup_credential() always rewrite all credentials
upon exec_invoke(), i.e. invocation of each ExecCommand, and within
a single tmpfs instance. This is problematic though:

* When writing each tmp cred file, we essentially double the size
  of the credential. Therefore, if one cred is bigger than half
  of CREDENTIALS_TOTAL_SIZE_MAX, confusing ENOSPC occurs (see also
  systemd#24734 (comment))

* Credential is a unit-wide thing and thus should not change
  during the whole lifetime of main process. However, if e.g.
  a on-disk credential or SetCredential= in unit file
  changes between ExecStart= and ExecStartPost=,
  the credentials are overwritten when the latter gets to run,
  and the already-running main process is suddenly seeing
  completely different creds.

So, let's try to reuse final cred dir if the main process has started
and the tmpfs has been populated, so that the creds used is stable
across all ExecStart= and ExecStartPost=-s. We still want to retain
the ability of updating creds through ExecStartPre= though, therefore
we forcibly use a fresh cred dir for those. 'Fresh' means to actually
unmount the old tmpfs first, so the first problem goes away, too.

fresh otherwise

Currently, exec_setup_credential() always rewrite all credentials
upon exec_invoke(), i.e. invocation of each ExecCommand, and within
a single tmpfs instance. This is problematic though:

* When writing each tmp cred file, we essentially double the size
  of the credential. Therefore, if one cred is bigger than half
  of CREDENTIALS_TOTAL_SIZE_MAX, confusing ENOSPC occurs (see also
  systemd#24734 (comment))

* Credential is a unit-wide thing and thus should not change
  during the whole lifetime of main process. However, if e.g.
  a on-disk credential or SetCredential= in unit file
  changes between ExecStart= and ExecStartPost=,
  the credentials are overwritten when the latter gets to run,
  and the already-running main process is suddenly seeing
  completely different creds.

So, let's try to reuse final cred dir if the main process has started
and the tmpfs has been populated, so that the creds used is stable
across all ExecStart= and ExecStartPost=-s. We still want to retain
the ability of updating creds through ExecStartPre= though, therefore
we forcibly use a fresh cred dir for those. 'Fresh' means to actually
unmount the old tmpfs first, so the first problem goes away, too.

fresh otherwise

Currently, exec_setup_credential() always rewrite all credentials
upon exec_invoke(), i.e. invocation of each ExecCommand, and within
a single tmpfs instance. This is problematic though:

* When writing each tmp cred file, we essentially double the size
  of the credential. Therefore, if one cred is bigger than half
  of CREDENTIALS_TOTAL_SIZE_MAX, confusing ENOSPC occurs (see also
  systemd#24734 (comment))

* Credential is a unit-wide thing and thus should not change
  during the whole lifetime of main process. However, if e.g.
  a on-disk credential or SetCredential= in unit file
  changes between ExecStart= and ExecStartPost=,
  the credentials are overwritten when the latter gets to run,
  and the already-running main process is suddenly seeing
  completely different creds.

So, let's try to reuse final cred dir if the main process has started
and the tmpfs has been populated, so that the creds used is stable
across all ExecStart= and ExecStartPost=-s. We still want to retain
the ability of updating creds through ExecStartPre= though, therefore
we forcibly use a fresh cred dir for those. 'Fresh' means to actually
unmount the old tmpfs first, so the first problem goes away, too.