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Re: [PATCH] avoid stat/fstat in statvfs/fstatvfs


Roland McGrath <roland@hack.frob.com> wrote:
> The substance of the change seems fine.  It needs a proper ChangeLog entry.
> See the glibc wiki for full instructions on posting patches.
> 
> > +  struct stat64 st;
> > +  int r = fd >= 0 ? fstat64(fd, &st) : stat64(name, &st);
> 
> Put space before paren in those calls.
> It's shorter and more common to invert the sense and use < 0.
> 
> > +  if (r == -1)
> >      return 0;
> 
> There is no need for a variable here.
> Also, it's more usual to test for failure with < 0:
> 
> 	if ((fd < 0 ? stat64 (name, &st) : fstat64 (fd, &st)) < 0)
> 	  return 0;

Thanks for the comments, here is an updated patch with your suggestions
and ChangeLog entry:

------------------------------- 8< ----------------------------
>From ed01f553461357e6c9ef40efd2910d897d72ddea Mon Sep 17 00:00:00 2001
From: Eric Wong <normalperson@yhbt.net>
Date: Fri, 1 Feb 2013 01:55:27 +0000
Subject: [PATCH] avoid stat/fstat in statvfs/fstatvfs

Delay the use of stat/fstat until stat data is required.
When the kernel returns ST_VALID, stat data is not used
by __internal_statvfs.

2013-02-07  Eric Wong  <normalperson@yhbt.net>

	* sysdeps/unix/sysv/linux/internal_statvfs.c (__statvfs_getflags):
	Call fstat64 or stat64 internally, depending on arguments passed.
	Replace stat buffer argument with file descriptor argument,
	update all callers.

diff --git a/sysdeps/unix/sysv/linux/fstatvfs.c b/sysdeps/unix/sysv/linux/fstatvfs.c
index 8f08d14..6a03a87 100644
--- a/sysdeps/unix/sysv/linux/fstatvfs.c
+++ b/sysdeps/unix/sysv/linux/fstatvfs.c
@@ -22,7 +22,7 @@
 #include <sys/statvfs.h>
 
 extern void __internal_statvfs (const char *name, struct statvfs *buf,
-				struct statfs *fsbuf, struct stat64 *st);
+				struct statfs *fsbuf, int fd);
 
 
 int
@@ -36,7 +36,7 @@ fstatvfs (int fd, struct statvfs *buf)
     return -1;
 
   /* Convert the result.  */
-  __internal_statvfs (NULL, buf, &fsbuf, fstat64 (fd, &st) == -1 ? NULL : &st);
+  __internal_statvfs (NULL, buf, &fsbuf, fd);
 
   /* We signal success if the statfs call succeeded.  */
   return 0;
diff --git a/sysdeps/unix/sysv/linux/fstatvfs64.c b/sysdeps/unix/sysv/linux/fstatvfs64.c
index 2dcef94..3b49ab2 100644
--- a/sysdeps/unix/sysv/linux/fstatvfs64.c
+++ b/sysdeps/unix/sysv/linux/fstatvfs64.c
@@ -25,7 +25,7 @@
 
 
 extern void __internal_statvfs64 (const char *name, struct statvfs64 *buf,
-				  struct statfs64 *fsbuf, struct stat64 *st);
+				  struct statfs64 *fsbuf, int fd);
 
 
 /* Return information about the filesystem on which FD resides.  */
@@ -60,12 +60,8 @@ __fstatvfs64 (int fd, struct statvfs64 *buf)
 #endif
 
   if (res == 0)
-    {
-      /* Convert the result.  */
-      struct stat64 st;
-      __internal_statvfs64 (NULL, buf, &fsbuf,
-			    fstat64 (fd, &st) == -1 ? NULL : &st);
-    }
+    /* Convert the result.  */
+    __internal_statvfs64 (NULL, buf, &fsbuf, fd);
 
   return res;
 }
diff --git a/sysdeps/unix/sysv/linux/internal_statvfs.c b/sysdeps/unix/sysv/linux/internal_statvfs.c
index 4cd4f04..1e1ad5f 100644
--- a/sysdeps/unix/sysv/linux/internal_statvfs.c
+++ b/sysdeps/unix/sysv/linux/internal_statvfs.c
@@ -43,9 +43,11 @@
 
 # ifndef __ASSUME_STATFS_F_FLAGS
 int
-__statvfs_getflags (const char *name, int fstype, struct stat64 *st)
+__statvfs_getflags (const char *name, int fstype, int fd)
 {
-  if (st == NULL)
+  struct stat64 st;
+
+  if ((fd < 0 ? stat64 (name, &st) : fstat64 (fd, &st)) < 0)
     return 0;
 
   const char *fsname = NULL;
@@ -153,7 +155,7 @@ __statvfs_getflags (const char *name, int fstype, struct stat64 *st)
 	  /* Find out about the device the current entry is for.  */
 	  struct stat64 fsst;
 	  if (stat64 (mntbuf.mnt_dir, &fsst) >= 0
-	      && st->st_dev == fsst.st_dev)
+	      && st.st_dev == fsst.st_dev)
 	    {
 	      /* Bingo, we found the entry for the device FD is on.
 		 Now interpret the option string.  */
@@ -216,14 +218,13 @@ __statvfs_getflags (const char *name, int fstype, struct stat64 *st)
 }
 # endif
 #else
-extern int __statvfs_getflags (const char *name, int fstype,
-			       struct stat64 *st);
+extern int __statvfs_getflags (const char *name, int fstype, int fd);
 #endif
 
 
 void
 INTERNAL_STATVFS (const char *name, struct STATVFS *buf,
-		  struct STATFS *fsbuf, struct stat64 *st)
+		  struct STATFS *fsbuf, int fd)
 {
   /* Now fill in the fields we have information for.  */
   buf->f_bsize = fsbuf->f_bsize;
@@ -266,7 +267,7 @@ INTERNAL_STATVFS (const char *name, struct STATVFS *buf,
        the /etc/mtab file and search for the entry which matches the given
        file.  The way we can test for matching filesystem is using the
        device number.  */
-    buf->f_flag = __statvfs_getflags (name, fsbuf->f_type, st);
+    buf->f_flag = __statvfs_getflags (name, fsbuf->f_type, fd);
   else
 #endif
     buf->f_flag = fsbuf->f_flags ^ ST_VALID;
diff --git a/sysdeps/unix/sysv/linux/statvfs.c b/sysdeps/unix/sysv/linux/statvfs.c
index 5d91d85..09b53f7 100644
--- a/sysdeps/unix/sysv/linux/statvfs.c
+++ b/sysdeps/unix/sysv/linux/statvfs.c
@@ -22,22 +22,20 @@
 #include <sys/statvfs.h>
 
 extern void __internal_statvfs (const char *name, struct statvfs *buf,
-				struct statfs *fsbuf, struct stat64 *st);
+				struct statfs *fsbuf, int fd);
 
 
 int
 statvfs (const char *file, struct statvfs *buf)
 {
   struct statfs fsbuf;
-  struct stat64 st;
 
   /* Get as much information as possible from the system.  */
   if (__statfs (file, &fsbuf) < 0)
     return -1;
 
   /* Convert the result.  */
-  __internal_statvfs (file, buf, &fsbuf,
-		      stat64 (file, &st) == -1 ? NULL : &st);
+  __internal_statvfs (file, buf, &fsbuf, -1);
 
   /* We signal success if the statfs call succeeded.  */
   return 0;
diff --git a/sysdeps/unix/sysv/linux/statvfs64.c b/sysdeps/unix/sysv/linux/statvfs64.c
index 42c1089..cd9a7ca 100644
--- a/sysdeps/unix/sysv/linux/statvfs64.c
+++ b/sysdeps/unix/sysv/linux/statvfs64.c
@@ -26,7 +26,7 @@
 
 
 extern void __internal_statvfs64 (const char *name, struct statvfs64 *buf,
-				  struct statfs64 *fsbuf, struct stat64 *st);
+				  struct statfs64 *fsbuf, int fd);
 
 
 /* Return information about the filesystem on which FILE resides.  */
@@ -61,12 +61,8 @@ __statvfs64 (const char *file, struct statvfs64 *buf)
 #endif
 
   if (res == 0)
-    {
-      /* Convert the result.  */
-      struct stat64 st;
-      __internal_statvfs64 (file, buf, &fsbuf,
-			    stat64 (file, &st) == -1 ? NULL : &st);
-    }
+    /* Convert the result.  */
+    __internal_statvfs64 (file, buf, &fsbuf, -1);
 
   return res;
 }
-- 
Eric Wong


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