Message ID | 20210329210928.561586-1-me@ikke.info (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | maintenance: specify explicit stdin for crontab | expand |
On Mon, 29 Mar 2021 at 23:23, Kevin Daudt <me@ikke.info> wrote: > > There are multiple crontab implementations that require stdin for > editing a crontab to be explicitly specified as '-'. [...] > --- a/t/helper/test-crontab.c > +++ b/t/helper/test-crontab.c > @@ -17,7 +17,7 @@ int cmd__crontab(int argc, const char **argv) > if (!from) > return 0; > to = stdout; > - } else if (argc == 2) { > + } else if ((argc == 3 && !strcmp(argv[2], "-")) || argc == 2) { > from = stdin; > to = fopen(argv[1], "w"); Would it make sense to make this } else if (argc == 3 && !strcmp(argv[2], "-")) { in order to make this test-tool as picky as possible and to only accept the kind of usage we want to (well, need to) use? The tests as they stand would still pass, which I think argues for us not really needing that "argc == 2". This would be followed by } else return error("unknown arguments"); which wouldn't be super helpful if you forgot the "-", but helpful enough for an internal test-tool, I guess. Speaking of usage and hints, there's "Usage: ..." in a comment at the top of this file. It should probably be updated either way. Martin
On 3/30/2021 1:41 AM, Martin Ågren wrote: > On Mon, 29 Mar 2021 at 23:23, Kevin Daudt <me@ikke.info> wrote: >> >> There are multiple crontab implementations that require stdin for >> editing a crontab to be explicitly specified as '-'. Thank you for reporting this, especially with a patch! However, I'm not sure about this adding of '-' being something that crontab ignores so commonly. My Ubuntu machine reports this: $ crontab -e - crontab: usage error: no arguments permitted after this option usage: crontab [-u user] file crontab [ -u user ] [ -i ] { -e | -l | -r } (default operation is replace, per 1003.2) -e (edit user's crontab) -l (list user's crontab) -r (delete user's crontab) -i (prompt before deleting user's crontab) Is there a way we could attempt writing over stdin, notice the failure, then retry with the '-' option? > > [...] > >> --- a/t/helper/test-crontab.c >> +++ b/t/helper/test-crontab.c >> @@ -17,7 +17,7 @@ int cmd__crontab(int argc, const char **argv) >> if (!from) >> return 0; >> to = stdout; >> - } else if (argc == 2) { >> + } else if ((argc == 3 && !strcmp(argv[2], "-")) || argc == 2) { >> from = stdin; >> to = fopen(argv[1], "w"); > > Would it make sense to make this > > } else if (argc == 3 && !strcmp(argv[2], "-")) { > > in order to make this test-tool as picky as possible and to only accept > the kind of usage we want to (well, need to) use? The tests as they > stand would still pass, which I think argues for us not really needing > that "argc == 2". > > This would be followed by > > } else > return error("unknown arguments"); > > which wouldn't be super helpful if you forgot the "-", but helpful > enough for an internal test-tool, I guess. > > Speaking of usage and hints, there's "Usage: ..." in a comment at the > top of this file. It should probably be updated either way. I agree with Martin's review here, too. Thanks, -Stolee
On Tue, Mar 30, 2021 at 08:02:22AM -0400, Derrick Stolee wrote: > On 3/30/2021 1:41 AM, Martin Ågren wrote: > > On Mon, 29 Mar 2021 at 23:23, Kevin Daudt <me@ikke.info> wrote: > >> > >> There are multiple crontab implementations that require stdin for > >> editing a crontab to be explicitly specified as '-'. > > Thank you for reporting this, especially with a patch! > > However, I'm not sure about this adding of '-' being something that > crontab ignores so commonly. My Ubuntu machine reports this: > > $ crontab -e - > crontab: usage error: no arguments permitted after this option > usage: crontab [-u user] file > crontab [ -u user ] [ -i ] { -e | -l | -r } > (default operation is replace, per 1003.2) > -e (edit user's crontab) > -l (list user's crontab) > -r (delete user's crontab) > -i (prompt before deleting user's crontab) > > Is there a way we could attempt writing over stdin, notice the > failure, then retry with the '-' option? We do not use -e to edit, we run `crontab` and provide the contents to stdin. `crontab -e` just opens the crontab in the users editor, which would work with busybox as well, but that's not what's being done here. > > > > > [...] > > > >> --- a/t/helper/test-crontab.c > >> +++ b/t/helper/test-crontab.c > >> @@ -17,7 +17,7 @@ int cmd__crontab(int argc, const char **argv) > >> if (!from) > >> return 0; > >> to = stdout; > >> - } else if (argc == 2) { > >> + } else if ((argc == 3 && !strcmp(argv[2], "-")) || argc == 2) { > >> from = stdin; > >> to = fopen(argv[1], "w"); > > > > Would it make sense to make this > > > > } else if (argc == 3 && !strcmp(argv[2], "-")) { > > > > in order to make this test-tool as picky as possible and to only accept > > the kind of usage we want to (well, need to) use? The tests as they > > stand would still pass, which I think argues for us not really needing > > that "argc == 2". > > > > This would be followed by > > > > } else > > return error("unknown arguments"); > > > > which wouldn't be super helpful if you forgot the "-", but helpful > > enough for an internal test-tool, I guess. > > > > Speaking of usage and hints, there's "Usage: ..." in a comment at the > > top of this file. It should probably be updated either way. > > I agree with Martin's review here, too. Yes, I agree too, was already contemplating that. > > Thanks, > -Stolee
Hi, Derrick Stolee wrote: > On 3/30/2021 1:41 AM, Martin Ågren wrote: >> On Mon, 29 Mar 2021 at 23:23, Kevin Daudt <me@ikke.info> wrote: >>> >>> There are multiple crontab implementations that require stdin for >>> editing a crontab to be explicitly specified as '-'. Amusingly, I wrote the exact same patch 2 weeks ago (including not dropping the `argc == 2` which Martin mentioned). That was in response to a report in the Fedora bugzilla: https://bugzilla.redhat.com/1939930 I thought cronie might be rather rare with it's non-POSIX handling of crontab without arguments. In the end, the cronie folks upstream adjusted things so that crontab behaves as defined by POSIX if stdin is not a TTY: https://github.com/cronie-crond/cronie/commit/8b0241f That allows cronie to behave more sensibly for interactive use without breaking tools like git maintenance. And it let me sidestep proposing a patch to git (or worse, maintaining it in the Fedora packages). But I didn't dig in to find out whether or how many other crontab implemntations had also eschewed the (rather poor) POSIX-confirming behavior. Knowing there are several among popular OS's makes it easy to see something like this patch being generally useful. Though, as Derrick notes below, we would break systems which implement crontab strictly per the POSIX spec. I don't know how many crontab's don't accept `-`. At the time, I checked on an older OmniOS system I had access to (based on Illumos/OpenSolaris) and it did not accept `-`. So my quick sample size of 3 (Fedora, CentOS, and OmniOS) I had a 1/3 failure rate. > Thank you for reporting this, especially with a patch! > > However, I'm not sure about this adding of '-' being something that > crontab ignores so commonly. My Ubuntu machine reports this: > > $ crontab -e - > crontab: usage error: no arguments permitted after this option > usage: crontab [-u user] file > crontab [ -u user ] [ -i ] { -e | -l | -r } > (default operation is replace, per 1003.2) > -e (edit user's crontab) > -l (list user's crontab) > -r (delete user's crontab) > -i (prompt before deleting user's crontab) > > Is there a way we could attempt writing over stdin, notice the > failure, then retry with the '-' option? You'd skip the `-e` there, no? Running `crontab -` in a current ubuntu container with the cron package installed (what looks like vixie-cron-3.0pl1) works as expected. Perhaps a Makefile knob to allow systems with such a crontab to adjust the behavior would be an alternative to detecting and retrying? NEEDS_CRONTAB_STDIN_OPT or something like that, with config.mak.uname to override whichever default is chosen. Whether that's a better option really depends on how much effort it is to add and maintain the detection in the code weighed against how many systems would need to have the default changed. Mildy related, I wonder whether we'll eventually see a patch to use systemd timers instead of cron (optionally, of course). Fedora, for example, doesn't install crond by default anymore. (Though, warts and all, I still prefer crond myself.) >> [...] >> >>> --- a/t/helper/test-crontab.c >>> +++ b/t/helper/test-crontab.c >>> @@ -17,7 +17,7 @@ int cmd__crontab(int argc, const char **argv) >>> if (!from) >>> return 0; >>> to = stdout; >>> - } else if (argc == 2) { >>> + } else if ((argc == 3 && !strcmp(argv[2], "-")) || argc == 2) { >>> from = stdin; >>> to = fopen(argv[1], "w"); >> >> Would it make sense to make this >> >> } else if (argc == 3 && !strcmp(argv[2], "-")) { >> >> in order to make this test-tool as picky as possible and to only accept >> the kind of usage we want to (well, need to) use? The tests as they >> stand would still pass, which I think argues for us not really needing >> that "argc == 2". >> >> This would be followed by >> >> } else >> return error("unknown arguments"); >> >> which wouldn't be super helpful if you forgot the "-", but helpful >> enough for an internal test-tool, I guess. >> >> Speaking of usage and hints, there's "Usage: ..." in a comment at the >> top of this file. It should probably be updated either way. > > I agree with Martin's review here, too.
On 3/30/2021 1:12 PM, Kevin Daudt wrote: > On Tue, Mar 30, 2021 at 08:02:22AM -0400, Derrick Stolee wrote: >> On 3/30/2021 1:41 AM, Martin Ågren wrote: >>> On Mon, 29 Mar 2021 at 23:23, Kevin Daudt <me@ikke.info> wrote: >>>> >>>> There are multiple crontab implementations that require stdin for >>>> editing a crontab to be explicitly specified as '-'. >> >> Thank you for reporting this, especially with a patch! >> >> However, I'm not sure about this adding of '-' being something that >> crontab ignores so commonly. My Ubuntu machine reports this: >> >> $ crontab -e - >> crontab: usage error: no arguments permitted after this option >> usage: crontab [-u user] file >> crontab [ -u user ] [ -i ] { -e | -l | -r } >> (default operation is replace, per 1003.2) >> -e (edit user's crontab) >> -l (list user's crontab) >> -r (delete user's crontab) >> -i (prompt before deleting user's crontab) >> >> Is there a way we could attempt writing over stdin, notice the >> failure, then retry with the '-' option? > > We do not use -e to edit, we run `crontab` and provide the contents to > stdin. `crontab -e` just opens the crontab in the users editor, which > would work with busybox as well, but that's not what's being done here. Thank you. Of course. Muscle memory from testing crontab manually. Thanks, -Stolee
On 3/30/2021 1:43 PM, Todd Zullinger wrote: > Hi, > > Derrick Stolee wrote: >> On 3/30/2021 1:41 AM, Martin Ågren wrote: >>> On Mon, 29 Mar 2021 at 23:23, Kevin Daudt <me@ikke.info> wrote: >>>> >>>> There are multiple crontab implementations that require stdin for >>>> editing a crontab to be explicitly specified as '-'. > > Amusingly, I wrote the exact same patch 2 weeks ago > (including not dropping the `argc == 2` which Martin > mentioned). That was in response to a report in the Fedora > bugzilla: > > https://bugzilla.redhat.com/1939930 > > I thought cronie might be rather rare with it's non-POSIX > handling of crontab without arguments. Thanks for this link! I appreciate the context. > In the end, the cronie folks upstream adjusted things so > that crontab behaves as defined by POSIX if stdin is not a > TTY: > > https://github.com/cronie-crond/cronie/commit/8b0241f >> That allows cronie to behave more sensibly for interactive > use without breaking tools like git maintenance. And it let > me sidestep proposing a patch to git (or worse, maintaining > it in the Fedora packages). Nice! > But I didn't dig in to find out whether or how many other > crontab implemntations had also eschewed the (rather poor) > POSIX-confirming behavior. Knowing there are several among > popular OS's makes it easy to see something like this patch > being generally useful. > > Though, as Derrick notes below, we would break systems which > implement crontab strictly per the POSIX spec. I don't know > how many crontab's don't accept `-`. > > At the time, I checked on an older OmniOS system I had > access to (based on Illumos/OpenSolaris) and it did not > accept `-`. So my quick sample size of 3 (Fedora, CentOS, > and OmniOS) I had a 1/3 failure rate. > >> Thank you for reporting this, especially with a patch! >> >> However, I'm not sure about this adding of '-' being something that >> crontab ignores so commonly. My Ubuntu machine reports this: >> >> $ crontab -e - >> crontab: usage error: no arguments permitted after this option >> usage: crontab [-u user] file >> crontab [ -u user ] [ -i ] { -e | -l | -r } >> (default operation is replace, per 1003.2) >> -e (edit user's crontab) >> -l (list user's crontab) >> -r (delete user's crontab) >> -i (prompt before deleting user's crontab) >> >> Is there a way we could attempt writing over stdin, notice the >> failure, then retry with the '-' option? > > You'd skip the `-e` there, no? Running `crontab -` in a > current ubuntu container with the cron package installed > (what looks like vixie-cron-3.0pl1) works as expected. Yes, this is my mistake. My machine supports "crontab -". > Perhaps a Makefile knob to allow systems with such a crontab > to adjust the behavior would be an alternative to detecting > and retrying? > > NEEDS_CRONTAB_STDIN_OPT or something like that, with > config.mak.uname to override whichever default is chosen. > Whether that's a better option really depends on how much > effort it is to add and maintain the detection in the code > weighed against how many systems would need to have the > default changed. > > Mildy related, I wonder whether we'll eventually see a patch > to use systemd timers instead of cron (optionally, of > course). Fedora, for example, doesn't install crond by > default anymore. (Though, warts and all, I still prefer > crond myself.) Perhaps the best way to approach this is to try adding '-' by default, and remove it and try again on a failure. If the usage is actually a problem, that first command should fail quickly. I'm not sure if we could rely upon a specific category of error codes or if we should just say "non-zero exit means retry". Thanks! -Stolee
diff --git a/builtin/gc.c b/builtin/gc.c index ef7226d7b..dfdb5bce9 100644 --- a/builtin/gc.c +++ b/builtin/gc.c @@ -1904,6 +1904,7 @@ static int crontab_update_schedule(int run_maintenance, int fd, const char *cmd) rewind(cron_list); strvec_split(&crontab_edit.args, cmd); + strvec_push(&crontab_edit.args, "-"); crontab_edit.in = -1; crontab_edit.git_cmd = 0; diff --git a/t/helper/test-crontab.c b/t/helper/test-crontab.c index e7c0137a4..525cb318a 100644 --- a/t/helper/test-crontab.c +++ b/t/helper/test-crontab.c @@ -17,7 +17,7 @@ int cmd__crontab(int argc, const char **argv) if (!from) return 0; to = stdout; - } else if (argc == 2) { + } else if ((argc == 3 && !strcmp(argv[2], "-")) || argc == 2) { from = stdin; to = fopen(argv[1], "w"); } else