| Age | Commit message (Collapse) | Author | Lines |
|---|
|
POSIX requires pwrite to honor the explicit file offset where the
write should take place even if the file was opened as O_APPEND.
however, linux historically defined the pwrite syscall family as
honoring O_APPEND. this cannot be changed on the kernel side due to
stability policy, but the addition of the pwritev2 syscall with a
flags argument opened the door to fixing it, and linux commit
73fa7547c70b32cc69685f79be31135797734eb6 adds the RWF_NOAPPEND flag
that lets us request a write honoring the file offset argument.
this patch changes the pwrite function to first attempt using the
pwritev2 syscall with RWF_NOAPPEND, falling back to using the old
pwrite syscall only after checking that O_APPEND is not set for the
open file. if O_APPEND is set, the operation fails with EOPNOTSUPP,
reflecting that the kernel does not support the correct behavior. this
is an extended error case needed to avoid the wrong behavior that
happened before (writing the data at the wrong location), and is
aligned with the spirit of the POSIX requirement that "An attempt to
perform a pwrite() on a file that is incapable of seeking shall result
in an error."
since the pwritev2 syscall interprets the offset of -1 as a request to
write at the current file offset, it is mapped to a different negative
value that will produce the expected error.
pwritev, though not governed by POSIX at this time, is adjusted to
match pwrite in honoring the offset.
|
|
originally the namespace-infringing "large file support" interfaces
were included as part of glibc-ABI-compat, with the intent that they
not be used for linking, since our off_t is and always has been
unconditionally 64-bit and since we usually do not aim to support
nonstandard interfaces when there is an equivalent standard interface.
unfortunately, having the symbols present and available for linking
caused configure scripts to detect them and attempt to use them
without declarations, producing all the expected ill effects that
entails.
as a result, commit 2dd8d5e1b8ba1118ff1782e96545cb8a2318592c was made
to prevent this, using macros to redirect the LFS64 names to the
standard names, conditional on _GNU_SOURCE or _LARGEFILE64_SOURCE.
however, this has turned out to be a source of further problems,
especially since g++ defines _GNU_SOURCE by default. in particular,
the presence of these names as macros breaks a lot of valid code.
this commit removes all the LFS64 symbols and replaces them with a
mechanism in the dynamic linker symbol lookup failure path to retry
with the spurious "64" removed from the symbol name. in the future,
if/when the rest of glibc-ABI-compat is moved out of libc, this can be
removed.
|
|
the LFS64 macro was not self-documenting and barely saved any
characters. simply use weak_alias directly so that it's clear what's
being done, and doesn't depend on a header to provide a strange macro.
|
|
|
|
|
