sh: Make <&0 disable the </dev/null implicit in a background command.

Although <&0 does nothing, it is a redirection affecting standard input and
should therefore disable the </dev/null redirection

sh: Make <&0 disable the </dev/null implicit in a background command.

Although <&0 does nothing, it is a redirection affecting standard input and
should therefore disable the </dev/null redirection implicit in a background
command.

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Merge head r233826 through r256722.

IFC @256277

Approved by: ken (mentor)

IFC @ r255692

Comment out IA32_MISC_ENABLE MSR access - this doesn't exist on AMD.
Need to sort out how arch-specific MSRs will be handled.

Merge from head

IFC @ r255209

sh: Remove unnecessary reset functions.

These are already handled by exception handlers.

IFC @ r254014

IFC @ r253862

- change the SI_SUB_RUN_SCHEDULER sysinits in hv_utilc and
hv_netvsc_drv_freebsd.c to SI_SUB_KTHREAD_IDLE, since the
former is no longer in FreeBSD.
The use of these SYSINITs can pro

IFC @ r253862

- change the SI_SUB_RUN_SCHEDULER sysinits in hv_utilc and
hv_netvsc_drv_freebsd.c to SI_SUB_KTHREAD_IDLE, since the
former is no longer in FreeBSD.
The use of these SYSINITs can probably be removed.

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sh: Remove #define MKINIT.

MKINIT only served for the removed mkinit. Many variables can be static now.

sh: Remove mkinit.

Replace the RESET blocks with regular functions and a reset() function that
calls them all.

This code generation tool is unusual and does not appear to provide much
benefit. I do

sh: Remove mkinit.

Replace the RESET blocks with regular functions and a reset() function that
calls them all.

This code generation tool is unusual and does not appear to provide much
benefit. I do not think isolating the knowledge about which modules need to
be reset is worth an almost 500-line build tool and wider scope for
variables used by the reset functions.

Also, relying on reset functions is often wrong: the cleanup should be done
in exception handlers so that no stale state remains after 'command eval'
and the like.

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IFC @253398

Merge fresh head.

sh: Use O_CLOEXEC and F_DUPFD_CLOEXEC instead of separate fcntl() call.

sync from head

sh: Write as much into the heredoc pipe as possible, to avoid forking.

Use non-blocking I/O to write as much as the pipe will accept (often 64K,
but it can be as little as 4K), avoiding the need for

sh: Write as much into the heredoc pipe as possible, to avoid forking.

Use non-blocking I/O to write as much as the pipe will accept (often 64K,
but it can be as little as 4K), avoiding the need for the ugly PIPESIZE
constant. If PIPESIZE was set too high, a deadlock would occur.

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IFC @247348.

Sync with HEAD.

sh: Expand here documents in the current process.

Expand here documents at the same point other redirections are expanded but
use a non-fork subshell environment (like simple command substitutions)

sh: Expand here documents in the current process.

Expand here documents at the same point other redirections are expanded but
use a non-fork subshell environment (like simple command substitutions) for
compatibility. Substitition errors result in an empty here document like
before.

As a result, a fork is avoided for short (<4K) expanded here documents.

Unexpanded here documents (with quoted end marker after <<) are not affected
by this change. They already only forked when >4K.

Side effects:
* Order of expansion is slightly different.
* Slow expansions are not executed in parallel with the redirected command.
* A non-fork subshell environment is subtly different from a forked process.

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sh: Remove special code for shell scripts without magic number.

These are called "shell procedures" in the source.

If execve() failed with [ENOEXEC], the shell would reinitialize itself
and execute

sh: Remove special code for shell scripts without magic number.

These are called "shell procedures" in the source.

If execve() failed with [ENOEXEC], the shell would reinitialize itself
and execute the program as a script. This requires a fair amount of code
which is not frequently used (most scripts have a #! magic number).
Therefore just execute a new instance of sh (_PATH_BSHELL) to run the
script.

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sh: Check if dup2 for redirection from/to a file succeeds.

A failure (e.g. caused by ulimit -n being set very low) is a redirection
error.

Example:
ulimit -n 9; exec 9<.

Sync: merge r214221 through r214352 from ^/head.

sh: Check whether dup2 was successful for >&FD and <&FD.

A failure (usually caused by FD not being open) is a redirection error.

Exp-run done by: pav (with some other sh(1) changes)

In the spirit of r90111, depend on c89 and remove the "STATIC" macro
and its usage.

Consistently use "STATIC" for all functions in order to be able to set
breakpoints with in a debugger. And use naked "static" for variables.

Noticed by: bde