fix: O_ACCMODE flag handling in fdopen/fopen/fread/fwrite/fcntl - #437
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- fdopen/fopen: replace FLAG_IS_SET(open_mode, O_RDONLY) with O_ACCMODE mask comparison. FLAG_IS_SET with O_RDONLY=0 always returns true, causing IOBF_READ to be set on write-only streams. - fcntl F_GETFL: include O_RDONLY/O_WRONLY/O_RDWR and O_APPEND bits in the returned flags. Previously F_GETFL only returned O_NONBLOCK/ O_ASYNC/O_PATH, breaking the BFD-style 'fdflags & O_ACCMODE' switch. - fread: move cantread() check before the fast path. The fast path bypassed cantread when the buffer was already allocated, allowing reads on write-only streams to silently succeed. - fwrite: add cantwrite() check before the fast path, symmetric with the fread fix. - test_programs/unistd/fdopen_flags.c: new test covering all fdopen mode strings and the fcntl(F_GETFL)+O_ACCMODE pattern used by BFD.
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fdopen/fopen: replace FLAG_IS_SET(open_mode, O_RDONLY) with O_ACCMODE mask comparison. FLAG_IS_SET with O_RDONLY=0 always returns true, causing IOBF_READ to be set on write-only streams.
fcntl F_GETFL: include O_RDONLY/O_WRONLY/O_RDWR and O_APPEND bits in the returned flags. Previously F_GETFL only returned O_NONBLOCK/ O_ASYNC/O_PATH, breaking the BFD-style 'fdflags & O_ACCMODE' switch.
fread: move cantread() check before the fast path. The fast path bypassed cantread when the buffer was already allocated, allowing reads on write-only streams to silently succeed.
fwrite: add cantwrite() check before the fast path, symmetric with the fread fix.
test_programs/unistd/fdopen_flags.c: new test covering all fdopen mode strings and the fcntl(F_GETFL)+O_ACCMODE pattern used by BFD.