From 6b2f3d1f769be5779b479c37800229d9a4809fc3 Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Tue, 27 Oct 2009 11:05:28 +0100 Subject: vfs: Implement proper O_SYNC semantics While Linux provided an O_SYNC flag basically since day 1, it took until Linux 2.4.0-test12pre2 to actually get it implemented for filesystems, since that day we had generic_osync_around with only minor changes and the great "For now, when the user asks for O_SYNC, we'll actually give O_DSYNC" comment. This patch intends to actually give us real O_SYNC semantics in addition to the O_DSYNC semantics. After Jan's O_SYNC patches which are required before this patch it's actually surprisingly simple, we just need to figure out when to set the datasync flag to vfs_fsync_range and when not. This patch renames the existing O_SYNC flag to O_DSYNC while keeping it's numerical value to keep binary compatibility, and adds a new real O_SYNC flag. To guarantee backwards compatiblity it is defined as expanding to both the O_DSYNC and the new additional binary flag (__O_SYNC) to make sure we are backwards-compatible when compiled against the new headers. This also means that all places that don't care about the differences can just check O_DSYNC and get the right behaviour for O_SYNC, too - only places that actuall care need to check __O_SYNC in addition. Drivers and network filesystems have been updated in a fail safe way to always do the full sync magic if O_DSYNC is set. The few places setting O_SYNC for lower layers are kept that way for now to stay failsafe. We enforce that O_DSYNC is set when __O_SYNC is set early in the open path to make sure we always get these sane options. Note that parisc really screwed up their headers as they already define a O_DSYNC that has always been a no-op. We try to repair it by using it for the new O_DSYNC and redefinining O_SYNC to send both the traditional O_SYNC numerical value _and_ the O_DSYNC one. Cc: Richard Henderson Cc: Ivan Kokshaysky Cc: Grant Grundler Cc: "David S. Miller" Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: Thomas Gleixner Cc: Al Viro Cc: Andreas Dilger Acked-by: Trond Myklebust Acked-by: Kyle McMartin Acked-by: Ulrich Drepper Signed-off-by: Christoph Hellwig Signed-off-by: Andrew Morton Signed-off-by: Jan Kara --- drivers/char/mem.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'drivers/char/mem.c') diff --git a/drivers/char/mem.c b/drivers/char/mem.c index 30eff80fed6f..fba76fb55abf 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -43,7 +43,7 @@ static inline int uncached_access(struct file *file, unsigned long addr) { #if defined(CONFIG_IA64) /* - * On ia64, we ignore O_SYNC because we cannot tolerate memory attribute aliases. + * On ia64, we ignore O_DSYNC because we cannot tolerate memory attribute aliases. */ return !(efi_mem_attributes(addr) & EFI_MEMORY_WB); #elif defined(CONFIG_MIPS) @@ -56,9 +56,9 @@ static inline int uncached_access(struct file *file, unsigned long addr) #else /* * Accessing memory above the top the kernel knows about or through a file pointer - * that was marked O_SYNC will be done non-cached. + * that was marked O_DSYNC will be done non-cached. */ - if (file->f_flags & O_SYNC) + if (file->f_flags & O_DSYNC) return 1; return addr >= __pa(high_memory); #endif -- cgit v1.2.3