* [PATCH] (partly) fix posix_fallocate*
@ 2005-04-28 23:13 Jakub Jelinek
2005-05-03 15:09 ` Ulrich Drepper
0 siblings, 1 reply; 2+ messages in thread
From: Jakub Jelinek @ 2005-04-28 23:13 UTC (permalink / raw)
To: Ulrich Drepper, Roland McGrath; +Cc: Glibc hackers
Hi!
http://www.opengroup.org/onlinepubs/009695399/functions/posix_fallocate.html
says:
If the offset+ len is beyond the current file size, then posix_fallocate() shall adjust the file size to offset+ len.
Otherwise, the file size shall not be changed.
while current posix_fallocate extends the file up to about f_bsize bytes
smaller size, say posix_fallocate (fd, 0, 10000) will result in 8191 bytes
long file.
Another problem is that if offset is < st.st_size, it will happily overwrite
some bytes in the file, while I can't find any wording that would allow to
modify the file content (other than extending it to offset+len if
smaller).
There is obviously another major problem, the lack of atomicity,
but that can be only solved by a kernel syscall.
2005-04-29 Jakub Jelinek <jakub@redhat.com>
* sysdeps/posix/posix_fallocate.c (posix_fallocate): If len == 0,
call ftruncate if offset is bigger than current size. Make sure
the file is offset + len bytes long if that is more than current size.
Don't overwrite previous content of the file.
* sysdeps/posix/posix_fallocate64.c (__posix_fallocate64_l64):
Likewise.
--- libc/sysdeps/posix/posix_fallocate.c.jj 2003-08-26 23:07:45.000000000 +0200
+++ libc/sysdeps/posix/posix_fallocate.c 2005-04-29 00:48:28.000000000 +0200
@@ -1,4 +1,4 @@
-/* Copyright (C) 2000, 2003 Free Software Foundation, Inc.
+/* Copyright (C) 2000, 2003, 2005 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
@@ -29,9 +29,8 @@ posix_fallocate (int fd, __off_t offset,
{
struct stat64 st;
struct statfs f;
- size_t step;
- /* `off_t´ is a signed type. Therefore we can determine whether
+ /* `off_t' is a signed type. Therefore we can determine whether
OFFSET + LEN is too large if it is a negative value. */
if (offset < 0 || len < 0)
return EINVAL;
@@ -47,24 +46,48 @@ posix_fallocate (int fd, __off_t offset,
if (! S_ISREG (st.st_mode))
return ENODEV;
+ if (len == 0)
+ {
+ if (st.st_size < offset)
+ {
+ int ret = __ftruncate (fd, offset);
+
+ if (ret != 0)
+ ret = errno;
+ return ret;
+ }
+ return 0;
+ }
+
/* We have to know the block size of the filesystem to get at least some
sort of performance. */
if (__fstatfs (fd, &f) != 0)
return errno;
- /* Align OFFSET to block size and adjust LEN. */
- step = (offset + f.f_bsize - 1) % ~f.f_bsize;
- offset += step;
+ /* Try to play safe. */
+ if (f.f_bsize == 0)
+ f.f_bsize = 512;
/* Write something to every block. */
- while (len > step)
+ for (offset += (len - 1) % f.f_bsize; len > 0; offset += f.f_bsize)
{
- len -= step;
+ len -= f.f_bsize;
+
+ if (offset < st.st_size)
+ {
+ unsigned char c;
+ ssize_t rsize = __pread (fd, &c, 1, offset);
+
+ if (rsize < 0)
+ return errno;
+ /* If there is a non-zero byte, the block must have been
+ allocated already. */
+ else if (rsize == 1 && c != 0)
+ continue;
+ }
if (__pwrite (fd, "", 1, offset) != 1)
return errno;
-
- offset += step;
}
return 0;
--- libc/sysdeps/posix/posix_fallocate64.c.jj 2004-03-10 10:32:05.000000000 +0100
+++ libc/sysdeps/posix/posix_fallocate64.c 2005-04-29 01:00:10.000000000 +0200
@@ -1,4 +1,4 @@
-/* Copyright (C) 2000, 2003, 2004 Free Software Foundation, Inc.
+/* Copyright (C) 2000, 2003, 2004, 2005 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
@@ -29,9 +29,8 @@ __posix_fallocate64_l64 (int fd, __off64
{
struct stat64 st;
struct statfs64 f;
- size_t step;
- /* `off64_t´ is a signed type. Therefore we can determine whether
+ /* `off64_t' is a signed type. Therefore we can determine whether
OFFSET + LEN is too large if it is a negative value. */
if (offset < 0 || len < 0)
return EINVAL;
@@ -47,24 +46,48 @@ __posix_fallocate64_l64 (int fd, __off64
if (! S_ISREG (st.st_mode))
return ENODEV;
+ if (len == 0)
+ {
+ if (st.st_size < offset)
+ {
+ int ret = __ftruncate64 (fd, offset);
+
+ if (ret != 0)
+ ret = errno;
+ return ret;
+ }
+ return 0;
+ }
+
/* We have to know the block size of the filesystem to get at least some
sort of performance. */
if (__fstatfs64 (fd, &f) != 0)
return errno;
- /* Align OFFSET to block size and adjust LEN. */
- step = (offset + f.f_bsize - 1) % ~f.f_bsize;
- offset += step;
+ /* Try to play safe. */
+ if (f.f_bsize == 0)
+ f.f_bsize = 512;
/* Write something to every block. */
- while (len > step)
+ for (offset += (len - 1) % f.f_bsize; len > 0; offset += f.f_bsize)
{
- len -= step;
+ len -= f.f_bsize;
+
+ if (offset < st.st_size)
+ {
+ unsigned char c;
+ ssize_t rsize = __pread64 (fd, &c, 1, offset);
+
+ if (rsize < 0)
+ return errno;
+ /* If there is a non-zero byte, the block must have been
+ allocated already. */
+ else if (rsize == 1 && c != 0)
+ continue;
+ }
if (__pwrite64 (fd, "", 1, offset) != 1)
return errno;
-
- offset += step;
}
return 0;
Jakub
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH] (partly) fix posix_fallocate*
2005-04-28 23:13 [PATCH] (partly) fix posix_fallocate* Jakub Jelinek
@ 2005-05-03 15:09 ` Ulrich Drepper
0 siblings, 0 replies; 2+ messages in thread
From: Ulrich Drepper @ 2005-05-03 15:09 UTC (permalink / raw)
To: Jakub Jelinek; +Cc: Glibc hackers
[-- Attachment #1: Type: text/plain, Size: 101 bytes --]
Applied.
--
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖
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[-- Type: application/pgp-signature, Size: 251 bytes --]
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