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lib/core: Optimize breaking hardlinks for regfiles 

It'd all be really nice if there was some sort of `O_TMPFILE` for symlinks, but
anyways the way we were doing a generic "make temp file than rename" actually
defeats some of the point of `O_TMPFILE`. It's now fully safe to do "copy to
self", so let's do that for regfiles.

Closes: #1378
Approved by: jlebon
This commit is contained in:
Colin Walters 2017-12-14 12:09:28 -05:00 committed by Atomic Bot
parent 4a2e08148d
commit 26b7637a39
1 changed files with 61 additions and 40 deletions
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101
src/libostree/ostree-core.c
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@ -749,6 +749,50 @@ ostree_content_file_parse (gboolean compressed,
cancellable, error); cancellable, error);
} }
static gboolean
break_symhardlink (int dfd,
const char *path,
struct stat *stbuf,
GLnxFileCopyFlags copyflags,
GCancellable *cancellable,
GError **error)
{
guint count;
gboolean copy_success = FALSE;
char *path_tmp = glnx_strjoina (path, ".XXXXXX");
for (count = 0; count < 100; count++)
{
g_autoptr(GError) tmp_error = NULL;
glnx_gen_temp_name (path_tmp);
if (!glnx_file_copy_at (dfd, path, stbuf, dfd, path_tmp, copyflags,
cancellable, &tmp_error))
{
if (g_error_matches (tmp_error, G_IO_ERROR, G_IO_ERROR_EXISTS))
continue;
g_propagate_error (error, g_steal_pointer (&tmp_error));
return FALSE;
}
copy_success = TRUE;
break;
}
if (!copy_success)
{
g_set_error (error, G_IO_ERROR, G_IO_ERROR_EXISTS,
"Exceeded limit of %u file creation attempts", count);
return FALSE;
}
if (!glnx_renameat (dfd, path_tmp, dfd, path, error))
return FALSE;
return TRUE;
}
/** /**
* ostree_break_hardlink: * ostree_break_hardlink:
* @dfd: Directory fd * @dfd: Directory fd
@ -784,48 +828,25 @@ gboolean ostree_break_hardlink (int dfd,
if (!glnx_fstatat (dfd, path, &stbuf, AT_SYMLINK_NOFOLLOW, error)) if (!glnx_fstatat (dfd, path, &stbuf, AT_SYMLINK_NOFOLLOW, error))
return FALSE; return FALSE;
if (!S_ISLNK (stbuf.st_mode) && !S_ISREG (stbuf.st_mode)) if (stbuf.st_nlink <= 1)
return TRUE; /* Note early return */
const GLnxFileCopyFlags copyflags = skip_xattrs ? GLNX_FILE_COPY_NOXATTRS : 0;
if (S_ISREG (stbuf.st_mode))
/* Note it's now completely safe to copy a file to itself,
* as glnx_file_copy_at() is documented to do an O_TMPFILE + rename()
* with GLNX_FILE_COPY_OVERWRITE.
*/
return glnx_file_copy_at (dfd, path, &stbuf, dfd, path,
copyflags | GLNX_FILE_COPY_OVERWRITE,
cancellable, error);
else if (S_ISLNK (stbuf.st_mode))
return break_symhardlink (dfd, path, &stbuf, copyflags,
cancellable, error);
else
return glnx_throw (error, "Unsupported type for entry '%s'", path); return glnx_throw (error, "Unsupported type for entry '%s'", path);
const GLnxFileCopyFlags copyflags =
skip_xattrs ? GLNX_FILE_COPY_NOXATTRS : 0;
if (stbuf.st_nlink > 1)
{
guint count;
gboolean copy_success = FALSE;
char *path_tmp = glnx_strjoina (path, ".XXXXXX");
for (count = 0; count < 100; count++)
{
g_autoptr(GError) tmp_error = NULL;
glnx_gen_temp_name (path_tmp);
if (!glnx_file_copy_at (dfd, path, &stbuf, dfd, path_tmp, copyflags,
cancellable, &tmp_error))
{
if (g_error_matches (tmp_error, G_IO_ERROR, G_IO_ERROR_EXISTS))
continue;
g_propagate_error (error, g_steal_pointer (&tmp_error));
return FALSE;
}
copy_success = TRUE;
break;
}
if (!copy_success)
{
g_set_error (error, G_IO_ERROR, G_IO_ERROR_EXISTS,
"Exceeded limit of %u file creation attempts", count);
return FALSE;
}
if (!glnx_renameat (dfd, path_tmp, dfd, path, error))
return FALSE;
}
return TRUE; return TRUE;
} }