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In a few places, we where using a fixed buffer of sizeof(Dir)+100
size for stat. This is not correct and fails if the name returned
in stat is long.
This results in being unable to seek to the end of file with a
long filename.
The kernel should do the same thing as dirfstat() from libc;
handling the conversion and buffer allocation and returning a
freeable Dir* pointer.
For this, a new dirchanstat() function was added.
The fstat syscall was not rewriting the name to the last path
element; fix it.
In addition, gracefully handle the mountfix case, reallocating
the buffer to accomidate the required stat length plus
size of the new name so dirsetname() does not fail.
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The Mhead structures have two sources of references to them:
- from Pgrp.mnthash hash-table
- from a channels Chan.umh pointer as returned by namec() for a union directory
Unless one holds the Mhead.lock RWLock, the Mhead.mount chain
can be mutated by eigther cmount(), cunmount() or closepgrp().
Readers, skipping acquiering the lock where:
mountfix(): responsible for rewriting directory entries for
union directory reads; was walking the Mhead.mount chain to
detect if the passed channel itself appears in the mount list.
cmount(): had a check and copy when "new" chan was a union itself
and if the MCREATE flag is set and would copy the mount table.
All this needs to be done with Mhead read-locked while copying
the mount entries.
devproc(): in the handler for reading /proc/n/ns file.
namec(): while checking if the Chan->umh should be initialized.
In addition to this, cmount() is changed to do the mountfree()
of the original mount chain when MREPL is done after releasing
the locks.
Also, some cosmetic changes...
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opening /fd, /srv and /shr
The OCEXEC flag used to be maintained per channel,
making it shared between all the file desciptors.
This has a unexpected side effects with regard to
channel passing drivers such as devdup (/fd),
devsrv (/srv) and devshr (/shr).
For example, opening a /srv file with OCEXEC
makes it impossible to be remounted by exportfs
as it internally does a exec() to mount and
re-export it. There is no way to reset the flag.
This change makes the OCEXEC flag per file descriptor,
so a open with the OCEXEC flag only affects the fd
group of the calling process, and not the channel
itself.
On rfork(RFFDG), the per file descriptor flags get
copied.
On dup(), the per file descriptor flags are reset.
The second modification is that /fd, /srv and /shr
should reject the ORCLOSE flag, as the files that
are returned have already been opend.
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reading directories with pread() offset has to work the same
way as read(), otherwise exportfs breaks rewinding in directories.
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forsyth)
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mflag field in what would be wasted as padding
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special case in namec()
we already export mntauth() and mntversion(), so why not stop
being sneaky and just export mntattach() so bindmount() and
devshr can just call it directly with proper arguments being
checked.
we can also avoid handling #M attach specially in namec()
by having the devmnt's attach function do error(Enoattach).
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as the Fgrp can be shared with other processes, we have to
recheck the fd index after locking the Fgrp in fdclose()
to make sure not to read beyond the bounds of the fd array.
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newchan()
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the new syscall is added under the symbol _nsec() for
binary compatibility.
nsec() is still a library function reading /dev/bintime.
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access to user memory can pagefault and newfd2() holds
fgrp spinlock while writing to it. make temporary copy
on the stack in syspipe().
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this change is in preparation for amd64. the systab calling
convention was also changed to return uintptr (as segattach
returns a pointer) and the arguments are now passed as
va_list which handles amd64 arguments properly (all arguments
are passed in 64bit quantities on the stack, tho the upper
part will not be initialized when the element is smaller
than 8 bytes).
this is partial. xalloc needs to be converted in the future.
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