From 73fa7547c70b32cc69685f79be31135797734eb6 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Mon, 31 Aug 2020 11:32:08 -0400 Subject: vfs: add RWF_NOAPPEND flag for pwritev2 The pwrite function, originally defined by POSIX (thus the "p"), is defined to ignore O_APPEND and write at the offset passed as its argument. However, historically Linux honored O_APPEND if set and ignored the offset. This cannot be changed due to stability policy, but is documented in the man page as a bug. Now that there's a pwritev2 syscall providing a superset of the pwrite functionality that has a flags argument, the conforming behavior can be offered to userspace via a new flag. Since pwritev2 checks flag validity (in kiocb_set_rw_flags) and reports unknown ones with EOPNOTSUPP, callers will not get wrong behavior on old kernels that don't support the new flag; the error is reported and the caller can decide how to handle it. Signed-off-by: Rich Felker Link: https://lore.kernel.org/r/20200831153207.GO3265@brightrain.aerifal.cx Reviewed-by: Jann Horn Signed-off-by: Christian Brauner --- include/linux/fs.h | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'include/linux') diff --git a/include/linux/fs.h b/include/linux/fs.h index ed5966a70495..4f7cfda29143 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -3335,6 +3335,8 @@ static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags) return 0; if (unlikely(flags & ~RWF_SUPPORTED)) return -EOPNOTSUPP; + if (unlikely((flags & RWF_APPEND) && (flags & RWF_NOAPPEND))) + return -EINVAL; if (flags & RWF_NOWAIT) { if (!(ki->ki_filp->f_mode & FMODE_NOWAIT)) @@ -3345,6 +3347,12 @@ static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags) if (flags & RWF_SYNC) kiocb_flags |= IOCB_DSYNC; + if ((flags & RWF_NOAPPEND) && (ki->ki_flags & IOCB_APPEND)) { + if (IS_APPEND(file_inode(ki->ki_filp))) + return -EPERM; + ki->ki_flags &= ~IOCB_APPEND; + } + ki->ki_flags |= kiocb_flags; return 0; } -- cgit v1.2.3