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utils, builder: Add wrappers for posix_fadvise.

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Add wrappers around posix_fadvise and use them in places we were
calling posix_fadvise directly before.

Also in virt-builder we were doing this (and ignoring the result):

  posix_fadvise (fd, 0, 0, POSIX_FADV_RANDOM|POSIX_FADV_DONTNEED);

However the POSIX_FADV_* flags are _not_ bitmasks!  In fact
POSIX_FADV_RANDOM|POSIX_FADV_DONTNEED == POSIX_FADV_NOREUSE so we were
giving a completely different hint from what we thought we were
giving.
This commit is contained in:
Richard W.M. Jones
2016-04-14 13:40:12 +01:00
parent eeacb4ef60
commit 83e92b4a97
4 changed files with 97 additions and 19 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
builder/pxzcat-c.c
View File

@@ -214,10 +214,7 @@ pxzcat (value filenamev, value outputfilev, unsigned nr_threads)
unix_error (err, (char *) "ftruncate", outputfilev);
}
#if defined HAVE_POSIX_FADVISE
/* Tell the kernel we won't read the output file. */
ignore_value (posix_fadvise (fd, 0, 0, POSIX_FADV_RANDOM|POSIX_FADV_DONTNEED));
#endif
guestfs_int_fadvise_noreuse (fd);
/* Iterate over blocks. */
iter_blocks (idx, nr_threads, filenamev, fd, outputfilev, ofd);

5
src/guestfs-internal-frontend.h
View File

@@ -87,6 +87,11 @@ extern int guestfs_int_is_true (const char *str);
extern const char *guestfs_int_ovmf_i386_firmware[];
extern const char *guestfs_int_ovmf_x86_64_firmware[];
extern const char *guestfs_int_aavmf_firmware[];
extern void guestfs_int_fadvise_sequential (int fd);
extern void guestfs_int_fadvise_random (int fd);
extern void guestfs_int_fadvise_noreuse (int fd);
//extern void guestfs_int_fadvise_dontneed (int fd);
extern void guestfs_int_fadvise_willneed (int fd);
/* These functions are used internally by the CLEANUP_* macros.
* Don't call them directly.

17
src/proto.c
View File

@@ -333,19 +333,6 @@ guestfs_int_send (guestfs_h *g, int proc_nr,
return serial;
}
static void
fadvise_sequential (int fd)
{
#if defined(HAVE_POSIX_FADVISE) && defined(POSIX_FADV_SEQUENTIAL)
/* Since the fd might be a non-file, eg. /dev/stdout, just ignore
* this when it fails. It's not clear from the man page, but the
* 'advice' parameter is NOT a bitmask. You can only pass one
* parameter with each call.
*/
ignore_value (posix_fadvise (fd, 0, 0, POSIX_FADV_SEQUENTIAL));
#endif
}
static int send_file_chunk (guestfs_h *g, int cancel, const char *buf, size_t len);
static int send_file_data (guestfs_h *g, const char *buf, size_t len);
static int send_file_cancellation (guestfs_h *g);
@@ -372,7 +359,7 @@ guestfs_int_send_file (guestfs_h *g, const char *filename)
return -1;
}
fadvise_sequential (fd);
guestfs_int_fadvise_sequential (fd);
/* Send file in chunked encoding. */
while (!g->user_cancel) {
@@ -829,7 +816,7 @@ guestfs_int_recv_file (guestfs_h *g, const char *filename)
goto cancel;
}
fadvise_sequential (fd);
guestfs_int_fadvise_sequential (fd);
/* Receive the file in chunked encoding. */
while ((r = receive_file_data (g, &buf)) > 0) {

89
src/utils.c
View File

@@ -35,6 +35,8 @@
#include <sys/wait.h>
#include <libintl.h>
#include "ignore-value.h"
/* NB: MUST NOT include "guestfs-internal.h" or gnulib headers. */
#include "guestfs.h"
#include "guestfs-internal-frontend.h"
@@ -385,3 +387,90 @@ guestfs_int_aavmf_firmware[] = {
NULL
};
/**
* Hint that we will read or write the file descriptor sequentially.
*
* It's OK to call this on a non-file since we ignore failure as it is
* only a hint.
*/
void
guestfs_int_fadvise_sequential (int fd)
{
#if defined(HAVE_POSIX_FADVISE) && defined(POSIX_FADV_SEQUENTIAL)
/* It's not clear from the man page, but the 'advice' parameter is
* NOT a bitmask. You can only pass one parameter with each call.
*/
ignore_value (posix_fadvise (fd, 0, 0, POSIX_FADV_SEQUENTIAL));
#endif
}
/**
* Hint that we will read or write the file descriptor randomly.
*
* It's OK to call this on a non-file since we ignore failure as it is
* only a hint.
*/
void
guestfs_int_fadvise_random (int fd)
{
#if defined(HAVE_POSIX_FADVISE) && defined(POSIX_FADV_RANDOM)
/* It's not clear from the man page, but the 'advice' parameter is
* NOT a bitmask. You can only pass one parameter with each call.
*/
ignore_value (posix_fadvise (fd, 0, 0, POSIX_FADV_RANDOM));
#endif
}
/**
* Hint that we will access the data only once.
*
* It's OK to call this on a non-file since we ignore failure as it is
* only a hint.
*/
void
guestfs_int_fadvise_noreuse (int fd)
{
#if defined(HAVE_POSIX_FADVISE) && defined(POSIX_FADV_NOREUSE)
/* It's not clear from the man page, but the 'advice' parameter is
* NOT a bitmask. You can only pass one parameter with each call.
*/
ignore_value (posix_fadvise (fd, 0, 0, POSIX_FADV_NOREUSE));
#endif
}
#if 0 /* not used yet */
/**
* Hint that we will not access the data in the near future.
*
* It's OK to call this on a non-file since we ignore failure as it is
* only a hint.
*/
void
guestfs_int_fadvise_dontneed (int fd)
{
#if defined(HAVE_POSIX_FADVISE) && defined(POSIX_FADV_DONTNEED)
/* It's not clear from the man page, but the 'advice' parameter is
* NOT a bitmask. You can only pass one parameter with each call.
*/
ignore_value (posix_fadvise (fd, 0, 0, POSIX_FADV_DONTNEED));
#endif
}
#endif
/**
* Hint that we will access the data in the near future.
*
* It's OK to call this on a non-file since we ignore failure as it is
* only a hint.
*/
void
guestfs_int_fadvise_willneed (int fd)
{
#if defined(HAVE_POSIX_FADVISE) && defined(POSIX_FADV_WILLNEED)
/* It's not clear from the man page, but the 'advice' parameter is
* NOT a bitmask. You can only pass one parameter with each call.
*/
ignore_value (posix_fadvise (fd, 0, 0, POSIX_FADV_WILLNEED));
#endif
}