This is very similar to write_string_file_atomic(), but is intentionally
kept separate (after long consideration). It focusses on arbitrary
struct iovec data, not just strings, and hence also doesn't do stdio at
all. It's hence a lot more low-level.
We might want to consider moving write_string_file*() on top of
write_data_file_atomic_at(), but for now don't.
Let's not leak details from src/shared and src/libsystemd into
src/basic, even though you can't actually do anything useful with
just forward declarations from src/shared.
The sd-forward.h header is put in src/libsystemd/sd-common as we
don't have a directory for shared internal headers for libsystemd
yet.
Let's also rename forward.h to basic-forward.h to keep things
self-explanatory.
As explained in https://lore.kernel.org/all/20250419183545.1982187-1-shakeel.butt@linux.dev/,
writing to memory.max or memory.high triggers synchronous memory reclaim
if the limit is lowered. This can end up taking nonnegligible amounts
of time, completely blocking pid1 from doing any other work while the
reclaim is ongoing.
To address this problem, the kernel going to add O_NONBLOCK semantics
to memory.max and memory.high. If the file is opened with O_NONBLOCK,
the synchronous memory reclaim is skipped and only triggered later
without blocking the process writing the file. Let's make sure we make
use of this by opening cgroupv2 attribute files with O_NONBLOCK.
We opt to do this for all cgroupv2 attribute files, to make sure that
if the same problem happens elsewhere in the future and is fixed in the
same way, we immediately take advantage of that fix without having to
make changes in systemd as well. We probably never want to block when
writing cgroupv2 attributes and any cases where we do want to block should
indicate so explicitly instead of blocking by default.
- Drop effectively unused "terminator" param, imply whitespace
- Make ret param optional
- Return ENODATA if the requested key is not found, rather than
ENOENT
- Turn ENOENT -> ENOSYS if /proc/ is not mounted
- Don't skip whitespaces before ':', nothing needs this handling
anyways
- Remove the special treatment for all "0"s. We don't actually
use this for capabilities given pidref_get_capability() exists
- Switch away from read_full_virtual_file() - files using "field"
scheme under /proc/ seem all to be "seq_file"s (refer to
da65941c3e for details on file types)
- Rename to script_get_shebang_interpreter and return
-EMEDIUMTYPE if the executable is not a script.
We nowadays utilize the scheme of making ret param
of getters optional, and use them directly as checkers.
- Don't unnecessarily read the whole line, but check
only the shebang first.
Given that we have the LabelOps abstraction these days, we can teach
write_string_file() to use it, which means we can get rid of
fileio-label.[ch] as a separate concept.
(The only reason that fileio-label.[ch] exists independently of
fileio.[ch] was that the former linekd to libselinux potentially, and
thus had to be in src/shared/ while the other always was in src/basic/.
But the LabelOps vtable provides us with a nice work-around)
let's rename the "_ts" flavour of these calls "_full" instead, exposing
the full functionality. And then keep two more minimal versions around:
one "_at" (which has the ts parameter suppressed, but keeps the dir_fd
one). And one without suffix (which supresses both).
Do the same for the label versions of these calls.
Let's modernize and clean up search_and_fopen a bit: let's add support
for regular open() (instead of fopen()), as well as access() (if caller
just wants to check if a file exists without opening it.
This unifies much of the code involved, which previously was duplicated
in search_and_fopen() and search_and_fopen_nulstr()
This is a combination of fdopen() and fd_reopen(). i.e. it first reopens
the fd, and then converts that into a FILE*.
We do this at various places already manually. let's move this into a
helper call of its own.
The data type off_t can be 64 on 32 bit systems if they have large
file support. Since mmap expects a size_t with 32 bits as second
argument truncation could occur. At worst these huge files could
lead to mmaps smaller than the previous check for small files.
This in turn shouldn't have a lot of impact because mmap allocates
at page size boundaries. This also made the PAGE_ALIGN call in
open_mmap unneeded. In fact it was neither in sync with other mmap
calls nor with its own munmap counterpart in error path.
If such large files are encountered, which is very unlikely in these
code paths, treat them with the same error as if they are too small.
It's so similar to copy_access(), hence let's move it over and rename it
in similar style to the rest of the functions.
No change in behaviour, just moving things over.
This beefs up the READ_FULL_FILE_CONNECT_SOCKET logic of
read_full_file_full() a bit: when used a sender socket name may be
specified. If specified as NULL behaviour is as before: the client
socket name is picked by the kernel. But if specified as non-NULL the
client can pick a socket name to use when connecting. This is useful to
communicate a minimal amount of metainformation from client to server,
outside of the transport payload.
Specifically, these beefs up the service credential logic to pass an
abstract AF_UNIX socket name as client socket name when connecting via
READ_FULL_FILE_CONNECT_SOCKET, that includes the requesting unit name
and the eventual credential name. This allows servers implementing the
trivial credential socket logic to distinguish clients: via a simple
getpeername() it can be determined which unit is requesting a
credential, and which credential specifically.
Example: with this patch in place, in a unit file "waldo.service" a
configuration line like the following:
LoadCredential=foo:/run/quux/creds.sock
will result in a connection to the AF_UNIX socket /run/quux/creds.sock,
originating from an abstract namespace AF_UNIX socket:
@$RANDOM/unit/waldo.service/foo
(The $RANDOM is replaced by some randomized string. This is included in
the socket name order to avoid namespace squatting issues: the abstract
socket namespace is open to unprivileged users after all, and care needs
to be taken not to use guessable names)
The services listening on the /run/quux/creds.sock socket may thus
easily retrieve the name of the unit the credential is requested for
plus the credential name, via a simpler getpeername(), discarding the
random preifx and the /unit/ string.
This logic uses "/" as separator between the fields, since both unit
names and credential names appear in the file system, and thus are
designed to use "/" as outer separators. Given that it's a good safe
choice to use as separators here, too avoid any conflicts.
This is a minimal patch only: the new logic is used only for the unit
file credential logic. For other places where we use
READ_FULL_FILE_CONNECT_SOCKET it is probably a good idea to use this
scheme too, but this should be done carefully in later patches, since
the socket names become API that way, and we should determine the right
amount of info to pass over.
Lennart Poettering
Lennart Poettering
Daan De Meyer
Mike Yuan
Yu Watanabe
gerblesh
Tobias Stoeckmann
Antony Deepak Thomas
Zbigniew Jędrzejewski-Szmek
David Seifert
williamvds