Re: [Qemu-devel] [PATCH v3 1/1] dump.c: allow fd_write_vmcore to return errno on failure
On 02/12/2018 03:31 PM, Eric Blake wrote: > On 02/12/2018 08:46 AM, Murilo Opsfelder Araujo wrote: >> On 02/12/2018 12:25 PM, Daniel Henrique Barboza wrote: >>> From: Yasmin Beatriz>>> >>> fd_write_vmcore can fail to execute for a lot of reasons that can be >>> retrieved by errno, but it only returns -1. This makes difficult for >>> the caller to know what happened and only a generic error message is >>> propagated back to the user. This is an example using dump-guest-memory: >>> > >>> +++ b/dump.c >>> @@ -107,7 +107,7 @@ static int fd_write_vmcore(const void *buf, >>> size_t size, void *opaque) >>> >>> written_size = qemu_write_full(s->fd, buf, size); >>> if (written_size != size) { >>> - return -1; >>> + return -errno; >>> } >>> >>> return 0; >>> @@ -140,7 +140,7 @@ static void write_elf64_header(DumpState *s, >>> Error **errp) >>> >>> ret = fd_write_vmcore(_header, sizeof(elf_header), s); >>> if (ret < 0) { >>> - error_setg(errp, "dump: failed to write elf header"); >>> + error_setg_errno(errp, -ret, "dump: failed to write elf >>> header"); >> >> Do we need -ret passed to error_setg_errno()? fd_write_vmcore() returns >> negative errno in case of error. > > Yes, this usage is correct. error_setg_errno() takes a positive errno > value (using strerror, which only decodes positive values into useful > strings); but we typically return negative errno values (as was > correctly done in fd_write_vmcore), so the extra layer of negation here > is needed. > For some reason I assumed "non-zero" in the error_setg_errno() description as negative. Thanks Daniel and Eric.
Re: [Qemu-devel] [PATCH v3 1/1] dump.c: allow fd_write_vmcore to return errno on failure
On 02/12/2018 08:25 AM, Daniel Henrique Barboza wrote: From: Yasmin Beatrizfd_write_vmcore can fail to execute for a lot of reasons that can be retrieved by errno, but it only returns -1. This makes difficult for the caller to know what happened and only a generic error message is propagated back to the user. This is an example using dump-guest-memory: (qemu) dump-guest-memory /home/yasmin/mnt/test.dump dump: failed to save memory ... This is the same dump-guest-memory example with this patch applied: (qemu) dump-guest-memory /home/yasmin/mnt/test.dump dump: failed to save memory: No space left on device (qemu) This example illustrates an error of fd_write_vmcore when called from write_data. All other callers will benefit from better error messages as well. Reported-by: yilzh...@redhat.com Cc: Jose Ricardo Ziviani Signed-off-by: Yasmin Beatriz Signed-off-by: Daniel Henrique Barboza --- dump.c | 23 ++- 1 file changed, 14 insertions(+), 9 deletions(-) Reviewed-by: Eric Blake -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
Re: [Qemu-devel] [PATCH v3 1/1] dump.c: allow fd_write_vmcore to return errno on failure
On 02/12/2018 08:46 AM, Murilo Opsfelder Araujo wrote: On 02/12/2018 12:25 PM, Daniel Henrique Barboza wrote: From: Yasmin Beatrizfd_write_vmcore can fail to execute for a lot of reasons that can be retrieved by errno, but it only returns -1. This makes difficult for the caller to know what happened and only a generic error message is propagated back to the user. This is an example using dump-guest-memory: +++ b/dump.c @@ -107,7 +107,7 @@ static int fd_write_vmcore(const void *buf, size_t size, void *opaque) written_size = qemu_write_full(s->fd, buf, size); if (written_size != size) { -return -1; +return -errno; } return 0; @@ -140,7 +140,7 @@ static void write_elf64_header(DumpState *s, Error **errp) ret = fd_write_vmcore(_header, sizeof(elf_header), s); if (ret < 0) { -error_setg(errp, "dump: failed to write elf header"); +error_setg_errno(errp, -ret, "dump: failed to write elf header"); Do we need -ret passed to error_setg_errno()? fd_write_vmcore() returns negative errno in case of error. Yes, this usage is correct. error_setg_errno() takes a positive errno value (using strerror, which only decodes positive values into useful strings); but we typically return negative errno values (as was correctly done in fd_write_vmcore), so the extra layer of negation here is needed. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
Re: [Qemu-devel] [PATCH v3 1/1] dump.c: allow fd_write_vmcore to return errno on failure
On 02/12/2018 12:46 PM, Murilo Opsfelder Araujo wrote: On 02/12/2018 12:25 PM, Daniel Henrique Barboza wrote: From: Yasmin Beatrizfd_write_vmcore can fail to execute for a lot of reasons that can be retrieved by errno, but it only returns -1. This makes difficult for the caller to know what happened and only a generic error message is propagated back to the user. This is an example using dump-guest-memory: (qemu) dump-guest-memory /home/yasmin/mnt/test.dump dump: failed to save memory All callers of fd_write_vmcore of dump.c does error handling via error_setg(), so at first it seems feasible to add the Error pointer as an argument of fd_write_vmcore. This proved to be more complex than it first looked. fd_write_vmcore is used by write_elf64_notes and write_elf32_notes as a WriteCoreDumpFunction prototype. WriteCoreDumpFunction is declared in include/qom/cpu.h and is used all around the code. This leaves us with few alternatives: - change the WriteCoreDumpFunction prototype to include an error pointer. This would require to change all functions that implements this prototype to also receive an Error pointer; - change both write_elf64_notes and write_elf32_notes to no use the WriteCoreDumpFunction. These functions use not only fd_write_vmcore but also buf_write_note, so this would require to change buf_write_note to handle an Error pointer. Considerable easier than the alternative above, but it's still a lot of code just for the benefit of the callers of fd_write_vmcore. This patch presents an easier solution that benefits all fd_write_vmcore callers: - instead of returning -1 on error, return -errno. All existing callers already checks for ret < 0 so there is no need to change the caller's logic too much. This also allows the retrieval of the errno. - all callers were updated to use error_setg_errno instead of just errno_setg. Now that fd_write_vmcore can return an errno, let's update all callers so they can benefit from a more detailed error message. This is the same dump-guest-memory example with this patch applied: (qemu) dump-guest-memory /home/yasmin/mnt/test.dump dump: failed to save memory: No space left on device (qemu) This example illustrates an error of fd_write_vmcore when called from write_data. All other callers will benefit from better error messages as well. Reported-by: yilzh...@redhat.com Cc: Jose Ricardo Ziviani Signed-off-by: Yasmin Beatriz Signed-off-by: Daniel Henrique Barboza --- dump.c | 23 ++- 1 file changed, 14 insertions(+), 9 deletions(-) diff --git a/dump.c b/dump.c index 7b13baa413..171ff8a3b8 100644 --- a/dump.c +++ b/dump.c @@ -107,7 +107,7 @@ static int fd_write_vmcore(const void *buf, size_t size, void *opaque) written_size = qemu_write_full(s->fd, buf, size); if (written_size != size) { -return -1; +return -errno; } return 0; @@ -140,7 +140,7 @@ static void write_elf64_header(DumpState *s, Error **errp) ret = fd_write_vmcore(_header, sizeof(elf_header), s); if (ret < 0) { -error_setg(errp, "dump: failed to write elf header"); +error_setg_errno(errp, -ret, "dump: failed to write elf header"); Do we need -ret passed to error_setg_errno()? fd_write_vmcore() returns negative errno in case of error. I am passing -ret here to provide a positive errno value to error_setg_errno. I am not sure if os_error can be negative and didn't want to risk strerror() breaking. Daniel Cheers Murilo
Re: [Qemu-devel] [PATCH v3 1/1] dump.c: allow fd_write_vmcore to return errno on failure
On 02/12/2018 12:25 PM, Daniel Henrique Barboza wrote: > From: Yasmin Beatriz> > fd_write_vmcore can fail to execute for a lot of reasons that can be > retrieved by errno, but it only returns -1. This makes difficult for > the caller to know what happened and only a generic error message is > propagated back to the user. This is an example using dump-guest-memory: > > (qemu) dump-guest-memory /home/yasmin/mnt/test.dump > dump: failed to save memory > > All callers of fd_write_vmcore of dump.c does error handling via > error_setg(), so at first it seems feasible to add the Error pointer as > an argument of fd_write_vmcore. This proved to be more complex than it > first looked. fd_write_vmcore is used by write_elf64_notes and > write_elf32_notes as a WriteCoreDumpFunction prototype. WriteCoreDumpFunction > is declared in include/qom/cpu.h and is used all around the code. This > leaves us with few alternatives: > > - change the WriteCoreDumpFunction prototype to include an error pointer. > This would require to change all functions that implements this prototype > to also receive an Error pointer; > > - change both write_elf64_notes and write_elf32_notes to no use the > WriteCoreDumpFunction. These functions use not only fd_write_vmcore > but also buf_write_note, so this would require to change buf_write_note > to handle an Error pointer. Considerable easier than the alternative > above, but it's still a lot of code just for the benefit of the callers > of fd_write_vmcore. > > This patch presents an easier solution that benefits all fd_write_vmcore > callers: > > - instead of returning -1 on error, return -errno. All existing callers > already checks for ret < 0 so there is no need to change the caller's > logic too much. This also allows the retrieval of the errno. > > - all callers were updated to use error_setg_errno instead of just > errno_setg. Now that fd_write_vmcore can return an errno, let's update > all callers so they can benefit from a more detailed error message. > > This is the same dump-guest-memory example with this patch applied: > > (qemu) dump-guest-memory /home/yasmin/mnt/test.dump > dump: failed to save memory: No space left on device > (qemu) > > This example illustrates an error of fd_write_vmcore when called > from write_data. All other callers will benefit from better > error messages as well. > > Reported-by: yilzh...@redhat.com > Cc: Jose Ricardo Ziviani > Signed-off-by: Yasmin Beatriz > Signed-off-by: Daniel Henrique Barboza > --- > dump.c | 23 ++- > 1 file changed, 14 insertions(+), 9 deletions(-) > > diff --git a/dump.c b/dump.c > index 7b13baa413..171ff8a3b8 100644 > --- a/dump.c > +++ b/dump.c > @@ -107,7 +107,7 @@ static int fd_write_vmcore(const void *buf, size_t size, > void *opaque) > > written_size = qemu_write_full(s->fd, buf, size); > if (written_size != size) { > -return -1; > +return -errno; > } > > return 0; > @@ -140,7 +140,7 @@ static void write_elf64_header(DumpState *s, Error **errp) > > ret = fd_write_vmcore(_header, sizeof(elf_header), s); > if (ret < 0) { > -error_setg(errp, "dump: failed to write elf header"); > +error_setg_errno(errp, -ret, "dump: failed to write elf header"); Do we need -ret passed to error_setg_errno()? fd_write_vmcore() returns negative errno in case of error. Cheers Murilo
Re: [Qemu-devel] [PATCH v3 1/1] dump.c: allow fd_write_vmcore to return errno on failure
Hi On Mon, Feb 12, 2018 at 3:25 PM, Daniel Henrique Barbozawrote: > From: Yasmin Beatriz > > fd_write_vmcore can fail to execute for a lot of reasons that can be > retrieved by errno, but it only returns -1. This makes difficult for > the caller to know what happened and only a generic error message is > propagated back to the user. This is an example using dump-guest-memory: > > (qemu) dump-guest-memory /home/yasmin/mnt/test.dump > dump: failed to save memory > > All callers of fd_write_vmcore of dump.c does error handling via > error_setg(), so at first it seems feasible to add the Error pointer as > an argument of fd_write_vmcore. This proved to be more complex than it > first looked. fd_write_vmcore is used by write_elf64_notes and > write_elf32_notes as a WriteCoreDumpFunction prototype. WriteCoreDumpFunction > is declared in include/qom/cpu.h and is used all around the code. This > leaves us with few alternatives: > > - change the WriteCoreDumpFunction prototype to include an error pointer. > This would require to change all functions that implements this prototype > to also receive an Error pointer; > > - change both write_elf64_notes and write_elf32_notes to no use the > WriteCoreDumpFunction. These functions use not only fd_write_vmcore > but also buf_write_note, so this would require to change buf_write_note > to handle an Error pointer. Considerable easier than the alternative > above, but it's still a lot of code just for the benefit of the callers > of fd_write_vmcore. > > This patch presents an easier solution that benefits all fd_write_vmcore > callers: > > - instead of returning -1 on error, return -errno. All existing callers > already checks for ret < 0 so there is no need to change the caller's > logic too much. This also allows the retrieval of the errno. > > - all callers were updated to use error_setg_errno instead of just > errno_setg. Now that fd_write_vmcore can return an errno, let's update > all callers so they can benefit from a more detailed error message. > > This is the same dump-guest-memory example with this patch applied: > > (qemu) dump-guest-memory /home/yasmin/mnt/test.dump > dump: failed to save memory: No space left on device > (qemu) > > This example illustrates an error of fd_write_vmcore when called > from write_data. All other callers will benefit from better > error messages as well. > > Reported-by: yilzh...@redhat.com > Cc: Jose Ricardo Ziviani > Signed-off-by: Yasmin Beatriz > Signed-off-by: Daniel Henrique Barboza lgtm, Reviewed-by: Marc-André Lureau > --- > dump.c | 23 ++- > 1 file changed, 14 insertions(+), 9 deletions(-) > > diff --git a/dump.c b/dump.c > index 7b13baa413..171ff8a3b8 100644 > --- a/dump.c > +++ b/dump.c > @@ -107,7 +107,7 @@ static int fd_write_vmcore(const void *buf, size_t size, > void *opaque) > > written_size = qemu_write_full(s->fd, buf, size); > if (written_size != size) { > -return -1; > +return -errno; > } > > return 0; > @@ -140,7 +140,7 @@ static void write_elf64_header(DumpState *s, Error **errp) > > ret = fd_write_vmcore(_header, sizeof(elf_header), s); > if (ret < 0) { > -error_setg(errp, "dump: failed to write elf header"); > +error_setg_errno(errp, -ret, "dump: failed to write elf header"); > } > } > > @@ -171,7 +171,7 @@ static void write_elf32_header(DumpState *s, Error **errp) > > ret = fd_write_vmcore(_header, sizeof(elf_header), s); > if (ret < 0) { > -error_setg(errp, "dump: failed to write elf header"); > +error_setg_errno(errp, -ret, "dump: failed to write elf header"); > } > } > > @@ -194,7 +194,8 @@ static void write_elf64_load(DumpState *s, MemoryMapping > *memory_mapping, > > ret = fd_write_vmcore(, sizeof(Elf64_Phdr), s); > if (ret < 0) { > -error_setg(errp, "dump: failed to write program header table"); > +error_setg_errno(errp, -ret, > + "dump: failed to write program header table"); > } > } > > @@ -217,7 +218,8 @@ static void write_elf32_load(DumpState *s, MemoryMapping > *memory_mapping, > > ret = fd_write_vmcore(, sizeof(Elf32_Phdr), s); > if (ret < 0) { > -error_setg(errp, "dump: failed to write program header table"); > +error_setg_errno(errp, -ret, > + "dump: failed to write program header table"); > } > } > > @@ -237,7 +239,8 @@ static void write_elf64_note(DumpState *s, Error **errp) > > ret = fd_write_vmcore(, sizeof(Elf64_Phdr), s); > if (ret < 0) { > -error_setg(errp, "dump: failed to write program header table"); > +error_setg_errno(errp, -ret, > + "dump: failed to write program header table"); > } > } > > @@ -302,7 +305,8 @@
[Qemu-devel] [PATCH v3 1/1] dump.c: allow fd_write_vmcore to return errno on failure
From: Yasmin Beatrizfd_write_vmcore can fail to execute for a lot of reasons that can be retrieved by errno, but it only returns -1. This makes difficult for the caller to know what happened and only a generic error message is propagated back to the user. This is an example using dump-guest-memory: (qemu) dump-guest-memory /home/yasmin/mnt/test.dump dump: failed to save memory All callers of fd_write_vmcore of dump.c does error handling via error_setg(), so at first it seems feasible to add the Error pointer as an argument of fd_write_vmcore. This proved to be more complex than it first looked. fd_write_vmcore is used by write_elf64_notes and write_elf32_notes as a WriteCoreDumpFunction prototype. WriteCoreDumpFunction is declared in include/qom/cpu.h and is used all around the code. This leaves us with few alternatives: - change the WriteCoreDumpFunction prototype to include an error pointer. This would require to change all functions that implements this prototype to also receive an Error pointer; - change both write_elf64_notes and write_elf32_notes to no use the WriteCoreDumpFunction. These functions use not only fd_write_vmcore but also buf_write_note, so this would require to change buf_write_note to handle an Error pointer. Considerable easier than the alternative above, but it's still a lot of code just for the benefit of the callers of fd_write_vmcore. This patch presents an easier solution that benefits all fd_write_vmcore callers: - instead of returning -1 on error, return -errno. All existing callers already checks for ret < 0 so there is no need to change the caller's logic too much. This also allows the retrieval of the errno. - all callers were updated to use error_setg_errno instead of just errno_setg. Now that fd_write_vmcore can return an errno, let's update all callers so they can benefit from a more detailed error message. This is the same dump-guest-memory example with this patch applied: (qemu) dump-guest-memory /home/yasmin/mnt/test.dump dump: failed to save memory: No space left on device (qemu) This example illustrates an error of fd_write_vmcore when called from write_data. All other callers will benefit from better error messages as well. Reported-by: yilzh...@redhat.com Cc: Jose Ricardo Ziviani Signed-off-by: Yasmin Beatriz Signed-off-by: Daniel Henrique Barboza --- dump.c | 23 ++- 1 file changed, 14 insertions(+), 9 deletions(-) diff --git a/dump.c b/dump.c index 7b13baa413..171ff8a3b8 100644 --- a/dump.c +++ b/dump.c @@ -107,7 +107,7 @@ static int fd_write_vmcore(const void *buf, size_t size, void *opaque) written_size = qemu_write_full(s->fd, buf, size); if (written_size != size) { -return -1; +return -errno; } return 0; @@ -140,7 +140,7 @@ static void write_elf64_header(DumpState *s, Error **errp) ret = fd_write_vmcore(_header, sizeof(elf_header), s); if (ret < 0) { -error_setg(errp, "dump: failed to write elf header"); +error_setg_errno(errp, -ret, "dump: failed to write elf header"); } } @@ -171,7 +171,7 @@ static void write_elf32_header(DumpState *s, Error **errp) ret = fd_write_vmcore(_header, sizeof(elf_header), s); if (ret < 0) { -error_setg(errp, "dump: failed to write elf header"); +error_setg_errno(errp, -ret, "dump: failed to write elf header"); } } @@ -194,7 +194,8 @@ static void write_elf64_load(DumpState *s, MemoryMapping *memory_mapping, ret = fd_write_vmcore(, sizeof(Elf64_Phdr), s); if (ret < 0) { -error_setg(errp, "dump: failed to write program header table"); +error_setg_errno(errp, -ret, + "dump: failed to write program header table"); } } @@ -217,7 +218,8 @@ static void write_elf32_load(DumpState *s, MemoryMapping *memory_mapping, ret = fd_write_vmcore(, sizeof(Elf32_Phdr), s); if (ret < 0) { -error_setg(errp, "dump: failed to write program header table"); +error_setg_errno(errp, -ret, + "dump: failed to write program header table"); } } @@ -237,7 +239,8 @@ static void write_elf64_note(DumpState *s, Error **errp) ret = fd_write_vmcore(, sizeof(Elf64_Phdr), s); if (ret < 0) { -error_setg(errp, "dump: failed to write program header table"); +error_setg_errno(errp, -ret, + "dump: failed to write program header table"); } } @@ -302,7 +305,8 @@ static void write_elf32_note(DumpState *s, Error **errp) ret = fd_write_vmcore(, sizeof(Elf32_Phdr), s); if (ret < 0) { -error_setg(errp, "dump: failed to write program header table"); +error_setg_errno(errp, -ret, + "dump: failed to write program header table"); } } @@ -355,7 +359,8 @@ static void